Lupine Publishers| Engineering Behavior of Warm Mix Asphalt Mixtures

 Lupine Publishers| Journal of Civil Engineering and its Architecture

Abstract

This paper presents the results of an extensive research that evaluated the laboratory characteristics of hot and warm mix asphalt mixtures manufactured with 100% virgin materials and with 15 and 35% recycled asphalt pavement. The overall objective of the study was to evaluate the engineering properties and performance characteristics of the mixtures while the specific objective was to assess the ability of the warm mix additives in allowing the use of higher content of recycled asphalt pavement without changing the performance grade of the virgin binder.

All mixtures were designed with the Marshall mix design method. The engineering properties consisted of the dynamic modulus master curve while the performance characteristics covered the mixtures resistances to moisture damage, rutting, thermal and fatigue cracking. The analysis of the data led to the following conclusions: warm mix additives were effective in moderating the increase in the engineering property of the mixtures containing 15 and 35% recycled asphalt pavement as compared to the hot mixtures without significantly reducing their resistance to rutting and thermal cracking, however, the warm mix additives were not capable of maintaining good resistance to fatigue cracking, therefore, the idea of using warm mix additives to allow higher recycled pavement in the asphalt mix is not supported by the measured resistance of the mixture to fatigue cracking.

Keywords: Warm mix; Recycled asphalt pavement; Marshall mix design; Dynamic modulus; Moisture damage; Rutting; Thermal and fatigue cracking

Introduction

Production of asphalt mixtures have always been challenging in terms of environmental friendliness and workers’ health. Various efforts are taken to address these concerns in paving industry. One of the approaches taken is to maximize the use of Recycled Asphalt Pavement (RAP) in asphalt mixtures, which helps in minimizing the use of natural asphalt binder and aggregates. Another approach is replacing Hot Mix Asphalt (HMA) with Warm Mix Asphalt (WMA) technologies, that lowers the production and laying temperatures of asphalt mixtures.

The majority of the states in US started using WMA and over 20WMA technologies are available in the US market. Boriak et al. conducted a laboratory study to examine the effect of 20 and 40% RAP contents on asphalt mixtures when the optimum asphalt binder is increased by 0.5% [1]. Evaluation of the mixtures were based on dynamic modulus, rutting resistance, and fatigue resistance of the asphalt concrete (AC) mixtures. An increase of 0.5% in the optimum asphalt binder content in mixtures with 0% and 20% RAP improved rutting and fatigue resistance of the mixtures while maintaining similar dynamic modulus. However, a significant drop in rutting resistance with no change in fatigue resistance was observed in the case of mixtures with 40% RAP.

Hajj et al. conducted a laboratory evaluation for the use of RAP in HMA mixtures [2]. Rutting, fatigue and thermal cracking, and moisture resistance characteristics of the HMA mixtures with 15 and 30% of RAP contents from three different sources were included in the evaluation. For polymer-modified mixtures, the study concluded that mixtures with 15 or 30% RAP will have an acceptable moisture resistance, equivalent rutting resistance, but reduced fatigue cracking resistance regardless of the sources of RAP.

Loria et al. evaluated asphalt mixtures with high RAP content in terms of resistance to moisture damage and thermal cracking [3]. Laboratory and field mixtures were compared based on their properties and performance. The research concluded that HMA mixtures with 50% RAP have acceptable resistance to thermal cracking and moisture damage. Measured Performance Grade (PG) temperatures from the recovered asphalt binder and the estimated critical temperatures from blending charts showed acceptable correlations. Overall, the study concluded that the resistance to moisture damage and thermal cracking of field produced asphalt mixtures can be evaluated from laboratory produced mixtures.

Objective and Scope

The objective of this study was to conduct comparative evaluations of mixtures that include various WMA technologies and different percentages of RAP. The research evaluated HMA and WMA mixtures from the “Spanish Springs” aggregate source, with three WMA technologies: Advera, Evotherm 3G, and Sonnewarmix and the HMA and WMA mixtures from the “Lockwood” aggregate source with the same three WMA technologies in addition to the Water Foam technology. Both aggregate sources are located in the northern part of the state of Nevada, USA and commonly used in the production of asphalt mixtures. All mixtures used the PG64-28NV polymer modified asphalt binder. Table 1 presents the summary of the experimental plan.

Table 1: Experimental Plan.

Materials Characterization

Aggregates

Table 2: Gradations of Spanish Springs Aggregates.

Table 3: Gradations of Lockwood Aggregates.

Aggregates used in this study were obtained from Spanish Springs and Lockwood sources. Five stockpiles of virgin aggregates and a RAP stockpile were used from each of the two aggregate sources. Aggregates blends were prepared from the aggregate stockpiles of each source that meet the Regional Transportation Commission (RTC) aggregate gradation specifications. Tables 2 & 3 present the bin percentages from the stockpiles and final gradation of the prepared blends. Specific gravity and relevant aggregate properties of various blends prepared are presented in the mix design summary. Difference in specific gravities among the stockpiles were less than 0.2, therefore, corrections of blend gradations were not required. Specific gravities of Spanish Springs aggregates were slightly higher than Lockwood aggregates. In addition, Lockwood aggregates had higher absorption compared to Spanish Springs aggregates. It should be noted that the aggregates were conditioned with hydrated lime for 48 hours prior to mixing process following the procedure specified in RTC specifications.

Asphalt Binder

The asphalt binder used for the study graded as PG64-28NV, which is a polymer modified asphalt binder. Performance grade (PG) of the asphalt binder was verified in the University laboratory following AASTHO M320 standard procedure. The actual grades for the asphalt binder were determined as 68.6 and -32.5 for the high and low temperatures, respectively. Range for mixing and compaction temperatures were provided by the supplier; 160 °C to 165 °C for mixing and 150 °C to 155 °C for compaction.

RAP Materials

RAP materials were collected from the Spanish Springs and Lockwood aggregate sources. Average asphalt binder contents for the Spanish Springs and Lockwood RAP were determined as 4.4% and 5.5% by dry weight of aggregate, respectively. Actual PGs for the Spanish Springs RAP binder were determined as PG87.9-27.8 whereas for the Lockwood RAP binder as PG85.3-26.3. Therefore, the standard PG of the RAP asphalt binders for both sources were identified as PG82-16. RAP aggregates were recovered and evaluated for gradation and specific gravity. The Nominal maximum size of both RAP aggregates was identified as 9.5mm. Absorption of the Lockwood RAP aggregates is higher than the absorption of the Spanish Springs RAP aggregates which was also the case for virgin aggregates.

Mix Designs

Nomenclature for the various mixtures were established according to the modification type and RAP aggregate percentage. For instance, HMAO, ADV15 and EVO35 represent HMA control mixture with no RAP, mixture with advera modification and 15 percent RAP, and mixture with evotherm modification and 35 percent RAP. Summary of the mixtures nomenclatures is presented in Table 4. Marshall Mix designs were conducted following the standard procedures established in the Asphalt Institute Manual “MS-2”, and criteria meeting the RTC specifications which are presented in Table 5. Mixing and compaction temperatures for the control mixtures were considered as provided by the supplier. However, for the WMA mixtures, mixing and compaction temperatures were selected at 135 °C and 120 °C, respectively, which are also the recommendation provided by the WMA technology suppliers. Table 5 summarizes the mix design results for both aggregate sources, three level of RAP contents, and various WMA technologies. It can be observed that the optimum binder content (OBC) at a specified air voids are higher for the Lockwood aggregate which is explained by its high absorption capacity compared to Spanish Springs Aggregate. All mixtures satisfy the requirement criteria for VMA, VFA, Marshall Stability, and Marshall Flow.

Table 4: Mixtures Nomenclatures.

Table 5: D Summary of Marshall Mix Designs.

For the Spanish Springs mixtures, the OBC for WMA mixtures with RAP were greater or similar to the HMA control mixtures. WMA mixtures were observed to have higher percentage of air voids at OBC than HMA control mixtures. It was also observed that, except for HMA control mixtures, air voids at OBC decreased with the increase in RAP content. Marshall Stability was observed to be increasing with the increment in RAP content. Also, WMA mixtures exhibited lower Marshall Stabilities compared to HMA mixtures. HMA mixtures have shown higher Marshall Flow than the WMA mixtures. However, a clear trend was not observed for the Marshall Flow with the percentage of RAP.

In the case of Lockwood mixtures, air voids at OBC for the HMA mixtures were observed lower than WMA mixtures. WMA mixtures had OBC higher than HMA mixtures by 0.2%, at all levels of RAP content. It was interesting to observe that the OBC for the 0 and 35% of RAP were similar, but the mixtures with 15% RAP had lower OBC. Trend for the Marshall Stability was similar to Spanish Spring mixtures. However, it was interesting to observe that the flow for mixtures with 15% RAP was lower than for the 0 and 35% RAP mixtures.

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Lupine Publishers| Effect of Brick Forming Load on Mechanical Properties of Fly-Ash Bricks

 Lupine Publishers| Journal of Civil Engineering and its Architecture

Abstract

Manufacturing of fly-ash bricks are the very useful alternatives of conventional burnt clay bricks. Manufacturing of clay bricks cause top soil removal, environmental pollution and health problems. To avoid all this environmental threats an attempt is made to manufacture of bricks using fly-ash, gypsum, sand and cement. Mainly fly-ash bricks are made by applying compressive load on the mold. In this research, the effect of brick forming load on the crushing load, water absorption and unit volume weight were studied. For this purpose bricks were prepared for different fly-ash (50% to 65% at 5% increments), gypsum (12% to 3% at 3% decrements), sand (28% to 22% at 2% decrements) and 10% cement. All ingredients were thoroughly mixed and then poured them to a mold of 9.5cm x 4.5cm x 2.75cm. Bricks were made by different forming load and mechanical properties were noted. This research suggested that it was possible to make good quality bricks using fly-ash, gypsum, sand and cement.

Keywords: Fly-ash; Gypsum; Sand; Cement; Brick forming load; Mechanical properties

Abbreviations: IS: Indian Standard

Introduction

Fly-ash is a predominantly inorganic residue obtained from the flue gases of furnaces at pulverized coal power plants. Fly-ash is produced in a large scale in all over the world. Production of fly-ash in different countries [1] is shown in Figure 1.

Figure 1: Fly ash production (Mg per year) and utilization (%) in different countries.

Now it has become a concern to dispose it in a right manner. For this many researchers have tried to found out the way to use them. Fly-ash is now used in different sectors like brick making, agriculture, concrete production, embankments, road pavement, mineral filler in asphaltic concrete, mine reclamation etc. Recent review such as [2,3] presented the possible applications of fly-ash. Fly-ash is now used in agriculture to increase the land properties [4]. Fly-ash has cementious properties. Thus, it has been used in making concrete [5]. Now fly-ash is disposed in the form of bricks. These bricks are made commercially in many countries like United Kingdom, Germany and India. Many solidifying agents are used in production of fly-ash bricks like lime [6], slag [7,8], dextrin [9] and gypsum [10,11]. Several numbers of patents on the use of fly-ash-lime mixures to make unfired bricks [12-15]. Gypsum is an important by-product of fertilizer industry and causes serious environmental problem [16]. The strength of fly ash-lime-gypsum (FaL-G) bricks and hollow blocks increased at a faster rate in initial days of curing and subsequently at a relatively lower rate. It was observed that the hot water curing leads to a greater degree of hardening and higher strength. Water absorption increases with increased fly ash content and it decreases with an increase in the density of FaL-G bricks and hollow blocks [17]. The strength of concrete increased with increasing amount of fly ash up to an optimum value and decreased with further addition of fly ash. The optimum value of fly ash for the test groups is about 40% of cement. Fly ash/cement ratio is an important factor determining the efficiency of fly ash [18]. The phenomenon of bond development between the fly ash-lime-gypsum (FaL-G) brick and the mortar. The morphological and microstructure studies of the brick-mortar interfaces clearly proved the chemical bond formation at the FaL-G brick-mortar interface [19]. The effect of incorporating various additives (i.e. cured resin, pulverized stone, pulverized plaster, and glass fibers) and two drying method (air and microwave) on compressive strength of gypsum products. Microwave drying for 5 minutes could fasten the drying time and permit early manipulation of plaster and stone models [20]. The addition of fly ash enhanced the quality of the brick, although for restoration purposes if too much fly ash (P10 wt.%) is added, this can spoil the aesthetic appearance of the buildings being restored, due to excessive color differences [21]. The replacement of raw materials of clay by fly ash to make fired bricks is an effectively measure of saving land and decreasing pollution. The sintering temperature of bricks with high replacing ratio of clay by fly ash was about 1050C, which was 50-100C higher than that of fired clay bricks. The fired bricks were of high compressive strength, no cracking, low water absorption, high fastness to efflorescence, no frost and high resistance to frost-melting [22]. A technique for producing concrete bricks and paving blocks using C&D wastes as recycled aggregates. The replacement of coarse and fine natural aggregates by recycled aggregates at the levels of 25% and 50% had little effect on the compressive strength of the bricks and blocks, but higher levels of replacement reduced the compressive strength [23]. The investigation of industrial wastes produced by phosphoric acid plants and boron concentrators was used in light brick production. The environmental need to utilize wastes that would be hazardous otherwise. The economy of possible use of these wastes is also of importance since the disposal of the wastes [24]. Fly-ash-gypsum bricks are used as a lightweight, heavy strength and low cost bricks. Reaction of gypsum are taken place in the presence of water. By the presence of water it forms crystalline material which is not strong enough to bear a good compressive strength but uses as a finishing materials. In the past fly-ash was released to environment. Fly ash is used as pozzolan to produce cement. Fly-ash with gypsum is made a tough material having good finishing.

Experimental Programme

Materials used

Fly-ash: Fly ash used in this research was collected from Noapara, Jessore which is imported from India. Specific gravity of fly-ash was 2.10. The chemical compositions of fly ash in India [25] are indicated in Table 1.

Table 1: Chemical composition of fly ash in India.

Gypsum: Chemically known as “Calcium sulphate hydrate”. This material is non-toxic and don’t create any harmful effect on the human body, environment, plant lifes and animals. Gypsum used in this research was collected from Noapara, Jessore. Specific gravity of gypsum was 2.34. The chemical compositions of natural gypsum [10] is indicated in Table 2.

Table 2: Chemical composition of natural gypsum.

^aLoss of ignition at 950 °C

^bLoss of ignition at 550 °C

Sand: Locally available sand were used in this study. The specific gravity of sand was 2.78 and fineness modulus was 2.34.

Cement: Cement is a binder, a substance used for construction that sets, hardens and adheres to other materials, binding them together. Ordinary Portland Cement was used in this study. The physical properties used are given in Table 3.

Table 3: Physical properties of ordinary Portland cement.

Proportion and mixing of raw materials: Different proportion are used to cast fly-ash bricks. Materials are used as a percentage of the volume of the mold. Percentage of materials required for fly-ash bricks and brick no. for each proportion in different curing process and curing period Table 4.

Table 4: Percentage of materials required for fly-ash bricks and brick no. for each proportion in different curing process and curing period.

The amount of ingredients was weighted then mixed thoroughly in a dry state. When the colour of the mixed was seemed to uniform then water was added. After addition of the required quantity of water the mixture was thoroughly mixed in a pan. The water content used in this study was 80ml. The mixture was again thoroughly mixed until the mixture attained a uniform consistency.

Preparation of mortar blocks

A brick mold of size 9.5cm x 4.5cm x 2.75cm was used in this study. Then the mortar was placed on the mold and compacted using digitec concrete compression machine. The load was applied with average time of 15 seconds to 20 seconds. Then the excess mortar was hand finished. Nine specimens were prepared for each proportion. After that the brick forming load from the screen of the digitec concrete compression machine was recorded.

Curing of brick sample: The brick sample was taken out from the mold after 10 minutes. After removal from the molds, the brick samples were kept for air drying for 2 days. After sufficient strength was gained some of these bricks were transferred to water for 14 days and others were kept in air.

Method of testing: Poping out from the water bowl after 14 days curing, bricks were tested for compressive strength using digitec concrete compression machine. Compressive strength and water absorption test were conducted by following IS:3495 [26] and unit volume weight was conducted using literature.

Results and Discussion

Effect of brick forming load on crushing load

Air curing: Table 5 gives the information of forming and crushing load on water curing fly-ash bricks while Figure 2 presents the graphical representation of table 5. In Figure 2, crushing load is experienced upward in the first and gradually decreasing to the last. On the other hand forming load is gradually upward. Brick No. A3 gives the highest crushing value from all the available bricks which is marked in the Table 5 while C1 shows lowest crushing value.

Table 5: Crushing Load (kN) for air curing fly-ash bricks.

Water curing: Table 6 illustrates the forming load as well as crushing of fly-ash bricks of water curing of 12 bricks while Figure 3 represent the graphical demonstration of Table 6. Figure 3 shows a variety of deflections in crushing load of fly-ash bricks. Brick No. A3 gives the maximum crushing value i.e., 62.5kN and D5 shows the lowest crushing value of about 31.28kN shown in Table 6. Both values are highlighted to visualize easily with graphical representation.

Figure 2: Variation of forming and crushing load for air curing fly ash bricks.

Figure 3: Variation of forming load and crushing load for water curing fly-ash bricks.

Table 6: Crushing Load (kN) for water curing fly-ash bricks.

Table 7: Forming load on water absorption of fly-ash bricks.

Effect of brick forming load on water absorption: Table 7 depicts the variation of water absorption in accordance with the brick forming load in a tabular format and with the help of these data a graph was plotted to easy visualization (Figure 4). Marked B9 and C7 shows lowest and highest water absorption respectively. The bar diagram shows almost same variations which is indicated in the Figure 4.

Figure 4: Variation of water absorption with respect to forming load of fly-ash bricks.

Effect of brick forming load on unit volume weight: Experimental data on conducting research on fly-ash bricks have been illustrated in a table format in Table 8 and a bar graph (Figure 5) was used to show the variation unit volume weight with the brick forming load. Though forming loads show a variations but unit volume weight seems like a plain straight.

Table 8: Forming load on unit volume weight of fly-ash bricks.

Figure 5: Variation of unit volume weight with respect to brick forming load of fly-ash bricks.

Conclusion

Usually, FA obtained high strength at the initial stage of the formation of fly ash bricks while FA need long term hydration for the FA. In this study, it is found that crushing load for the water curing is higher at the brick no. of A6 shown in the Table 6. For considering the air curing into account, and displayed maximum crushing load for the brick A3 shown in Table 5 and by bar diagram in Figure 2. The maximum crushing load for air and water curing for fly-ash bricks were 76 and 62.5kN respectively while minimum crushing load were 41.25 and 31.28kN for air and water curing respectively. By performing the comparison between air and water curing, an interesting outcome is found that crushing load for air is greater than the crushing load for water curing. It may be happened due to initial hydration effect of fly ash.

By taking water absorption, it is shown in Table 7 along with the Figure 4 that B9 and C7 gives the maximum and minimum water absorption respectively. Looking to the other bricks demonstrates almost same fluctuations of water absorption. Almost same results were found also in the unit weight of the fly ash bricks in which the results (Figure 5) displays the same height at the forming load.

By doing the study, it may be concluded that proportion for brick “A” is quite good rather than other bricks. More research should be conducted on fly ash bricks to attain more accurate results and relationship.

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Lupine Publishers| Influence of Fly Ash as Mineral Filler in Bituminous Mix Design

 Lupine Publishers| Journal of Civil Engineering and its Architecture

Abstract

Agricultural is the largest employment sector of Bangladesh and most of the people earn their living from agricultural production. The magnitude of agricultural production varies spatially as agricultural production depends on topography, the fertility of the land, availability of river, availability of marketing place, input and so on. The intent of our study is to regionalize all the 64 districts of Bangladesh based on Boro production, fish production and the number of growth center and to analyze the impact of it on rural development. To do so, the data are collected from the Bangladesh Bureau of Statistics (BBS), the composite index method was employed to analyze the data. The data reliability is checked through statistical parameters named level of skewness, kurtosis and standard error of the mean. Then acquired data is classified by using the mean standard deviation method, equal class interval method and the arithmetic mean method. Comparing the three histograms it is found that equal class interval method has more symmetrical shape, hence more normally distributed. Results show that most of the areas are moderately producing the agricultural product. The findings of this study can be used to find out the location which can be best suited for the agricultural industry.

Keywords: Optimum Bitumen Content; Optimum Fly Ash content; Stone Dust; Water Effect

Abbreviations: AASHTO: American Association of State Highway and Transportation Officials; BS: British Standard; CA: Coarse Aggregate; FA: Fine Aggregate; MF: Mineral Filler; OBC: Optimum Bitumen Content; Va: Voids in total Mix; VMA: Voids in Mineral Aggregate; VFB: Voids Filled with Bitumen

Introduction

The surface coarse of flexible pavement normally comprises of coarse aggregate, fine aggregate and filler heated to suitable temperature, mixed thoroughly with heated bitumen at required viscosity and then compacted [1]. One of the major concerns of mix design of bituminous mix is the type and amount of filler used which may affect the performance of the mix. Various studies have been conducted to study properties of mineral filler, generally the material passing 0.075mm IS sieve, to evaluate its effect on performance of asphalt paving mix in terms of consistency, void filling, Marshall Stability and mix strength. Fly ash is one of the major wastes by products of coal based thermal power station [2-5]. This waste is mostly disposed by coal-based thermal power plant in the form of refuse in piles and behind embankment type retaining structures. At present, with the expectation of small scales underground waste disposal operations in abandoned coal mines, most of this waste is disposed at the surface which inevitably requires excessive planning and control of minimize the environmental impact of mining. It also results in non-productive use of land, air and water pollution, possible failure of waste embankments and loss of aesthetic value of the land.

In recent years various research studies on fly ash have been conducted to analyze the possibility of utilization of these ashes. Hence, in this study, an attempt has been made to explore the use of fly ash passing 0.075mm sieve and has been considered to be filler in bituminous paving mixes by studying various fundamental engineering properties [6]. In recent years various researches have been conducted to use fly ash as mineral filler in bituminous mix design. Sankaran and Rao [7] made a comparison of fly ash with other fillers. They pointed out that fly ash at 2% filler content provided the highest stability among the other filler. Henning [8] investigated the effect of a class C fly ash on asphalt mixture properties and concluded that the addition of 4% fly ash resulted in the higher stability and flow but ended up with low air voids. Rosner et al. [9] used fly ash as mineral filler and anti-stripping agent for asphalt concrete mixtures and showed that retained strengths of samples increased as additional fly ash was used in the prepared mixtures.

Tapkin. showed that fly ash can be used effectively in a densedgraded wearing course as a filler replacement. Konstantin et al. studied on feasibility of fillers in asphalt concrete using two different binders. These binders were fully blended with filler materials i.e. fly ash, lime and cement [10]. The study result demonstrated that rheological properties of the asphalt were greatly improved with the addition of these fillers. Fly ash also appears in improving the aging resistance of mastics. With the addition of fillers, compatibility of mixtures was not affected Kar et al. represented the influence of fly ash as a filler as a filler in bituminous mixes that the mixes with fly ash as filler exhibits marginally inferior properties compared to control mixes and satisfy desired criteria specified by a much higher margin. They recommended to utilize fly ash wherever available, not only reducing the cost of execution, but also partly solve the fly ash utilization and disposal problem. Uddin and Supriya studied the influence of fillers on paving grade bitumen and observed that fly ash being a waste product can be effectively used as filler to improve the properties of bituminous mix and fly ash also being cost effective as compared to cement and lime.

Materials & Methodology

Materials Used

Table 1: Aggregate Gradation.

Aggregate: In the laboratory test program, black stone chips which are smaller than 25mm and larger than 2.36mm in size were regarded as coarse aggregate. The black stone used in this investigation was collected from construction site of architecture building of RUET. Aggregate gradation and physical properties of coarse aggregate are shown in Tables 1 & 2 respectively. The coarser sand smaller than 2.36mm and larger than 0.075mm in size were used as fine aggregate combination of domar sand and Padma river sand were used as the main source of fine aggregate. Specific gravity of fine aggregate was found to be 2.65. Two types of filler, stone dust and fly ash which is finer than 0.075mm in size a used in this investigation. Stone dust is used as standard filler for this project. Fly ash used for main purpose were collected from Barapukuria Coal Power Plant, Dinajpur. Here specific gravity of fly ash and stone dust were found to be 2.44 and 2.13 respectively [11].

Table 2: Properties of Coarse Aggregate.

Bitumen: Grade of 80/100 bitumen has been used as bitumen for preparation of bituminous mixture. The important physical properties are tabulated in Table 3.

Table 3: Properties of Bitumen.

Methodology

At first the test procedure introduced by Bruce Marshall and developed by the U.S Corps of Engineers was applied to find optimum bitumen content using stone dust as standard filler for medium traffic condition. This test has been fundamentally used in this study to evaluate the different mixture at different bitumen contents and the parameters considered are stability, flow value, unit weight, air voids, voids in mineral aggregates, voids filled with bitumen. Now by fixing this optimum bitumen content specimens were prepared. Specimens prepared by replacing stone dust with fly ash gradually such as 0% fly ash and 100% stone dust, 25% fly ash and 75% stone dust, 50% fly ash and 50% stone dust, 75% fly ash and 25% stone dust and 100% fly ash and 0% stone dust by total weight of filler. Bruce Marshall test was applied to determine optimum fly ash content by Marshall Mix design criteria for medium traffic condition [12]. Now using these optimum bitumen content and optimum fly ash content specimens were prepared to observe the effect of water submergence on compacted specimen. To observe the effect of water submergence on compacted specimen, compacted specimens were submerged in water for 0, 5, 10, 15 and 20 days. After each selected days Marshall Test was applied on these specimens.

Result and Discussion

Marshall Test of Specimens Using Stone Dust as Filler

For Bituminous mixes using standard filler stone dust and various bitumen content following six curves showing the relationships of unit weight, Marshall stability, flow, percentage of voids in total mix, percentage of voids in mineral aggregates, percentage of voids filled with bitumen with percentage of bitumen content were drown to determine optimum bitumen content. Curves were drown with data from Table 4. Curves are shown in Figures 1-6. Here, Optimum bitumen content from above figure calculated as 5.56%. Value of Stability, flow, %Va, %VMA and %VFB for optimum bitumen content satisfy the Marshall Mix Design Criteria.

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Lupine Publishers| Formal Region Delineation on the Basis of Agricultural Productivity and Growth Center

 Lupine Publishers| Journal of Civil Engineering and its Architecture

Abstract

Agricultural is the largest employment sector of Bangladesh and most of the people earn their living from agricultural production. The magnitude of agricultural production varies spatially as agricultural production depends on topography, the fertility of the land, availability of river, availability of marketing place, input and so on. The intent of our study is to regionalize all the 64 districts of Bangladesh based on Boro production, fish production and the number of growth center and to analyze the impact of it on rural development. To do so, the data are collected from the Bangladesh Bureau of Statistics (BBS), the composite index method was employed to analyze the data. The data reliability is checked through statistical parameters named level of skewness, kurtosis and standard error of the mean. Then acquired data is classified by using the mean standard deviation method, equal class interval method and the arithmetic mean method. Comparing the three histograms it is found that equal class interval method has more symmetrical shape, hence more normally distributed. Results show that most of the areas are moderately producing the agricultural product. The findings of this study can be used to find out the location which can be best suited for the agricultural industry.

Introduction

Since 2000, agriculture became a powerful driver for alleviating poverty in the rural economy of Bangladesh [1]. Rice and Jute are the primary crops. By utilizing the benefits of fertile soil and ample water supply, rice can be grown and harvested three times a year in many areas. It contributes 29% of gross domestic product and 63% people are engaged with agriculture. There have been several types of rice Aus, Amon, Boro etc. Among all these Boro crops contribute more. Fish is the second main food of Bangladesh. Bengalis cannot do much without rice and fish. Bangladesh is the 4^th largest fish producing country with a total production of around 3.26 Million Tones. In 2012, this sector contributed 4.4% of GDP and 23% of total agricultural production. So, it is clear that the agriculture of Bangladesh largely depends on Boro production and fish production which largely contribute to rural development. Growth center is the core of the trade of these agricultural products. In Bangladesh, the growth center basically refers to the rural markets which have been developed through the provision of infrastructure. In Bangladesh, there is total 3003 growth center [2]. So, the number of growth center largely contributes in rural trade. But agricultural production and distribution through growth center vary in different part of the country due to locational advantage or disadvantage, climate condition, and water availability. So, given that view, we explore formal regions based on Boro production, Fish production, and availability growth center. Thus, the level of rural development in the different region of Bangladesh. Because this type of formal regionalization is necessary to analyze the district from which we can get better feedback in terms of the agricultural industry. Agricultural industry gets influenced by several factors like prices of commodities, the farmers provide and are also associated with products obtained as a result of farming. Availability of growth center helps farmers to get adequate prices of their product. Through the establishment of agricultural industry, proper technology and training can be provided to further enrich the agricultural sector of those particular districts. Given that view, this study tries to identify the difference in agricultural production in the different district throughout the country.

Literature Review

Region means a large tract of land; a country; a more or less defined portion of earth’s surface, as distinguished by certain natural features, climatic conditions, a special fauna, and flora or the like [3]. The process of the delineating region is called regionalization. Regionalization can also be defined as a means of arranging the number of points on the earth surface and to observe the uniformities and regularities of phenomena upon it and to establish definite theories, models, systems, and structure. Before the industrial revolution, the purpose of delineation of the region was to find out the homogeneity of phenomena. The formal region is a geographical area which is uniform or homogeneous in terms of selected criteria such as topography, climate, industrial or agricultural-type [4]. Regions are treated as an important source of competition in economic geography [5]. According to J Glasson described “A formal region is a geographical area which is uniform or homogeneous in terms of selected criteria such as topography, climate, industrial or agricultural-type’’.

Regional development to some extent depends on the impact of the growth center. A center that contributes directly to the basic needs of agricultural producers, both in respect of economic and social services are termed as a growth center [6]. In rural areas, growth tends to concentrate in a center and influence the economy of surrounding areas. Also, growth center plays a significant role to spread growth in surrounding areas [7]. Smith used factor analysis method to identify areas of economic distress [8]. In his study, he divides the North West into several economic health, sub-regions using multiple socio-economic criteria. Flittie also observed the socioeconomic homogeneity using factor analysis method in Rocky Mountain West. The study shows that, physical regions which may or may not follow political boundaries-vary from the Western Hemisphere to the Great Plains to a river basin or watershed or to a national forest. Social and economic regions are equally diversefrom ethnic areas through Nob Hill and city ghetto and from the Common Market through national tariff barriers to regional and local trend centers.

(Mohiuddin & Bhuiya, 2013) has conducted a research on formal regionalization of Bangladesh and analyzes the dependencies of one region to another [9]. The intent of the study was to find out lack of the low productive regions. The study has divided the whole country into four regions which will be helpful for taking policy for the agricultural development on the basis of their production level. Crop productivity index and Moran-I statistics have been used in this study. Because of lack of all crops, they use different types of potato, Rice, jute, wheat etc. they consider four classes in data analysis. In this study, they found out that the south-east part of the country is low productive because of hilly terrain and natural disaster-prone area.

Methodology

The composite weighted index method has been used in this study to delineate formal region. The data for Boro production, Fish production and the number of growth center is collected from BBS 2011. These three variables have a positive correlation between them. That’s why these three variables are chosen for this study (Table 1).

Table 1: Correlation among variables.

After that, analyzing the selected three variables. From there, Log10 is calculated for every variable and (W1, W2, and W3) find out by the ratio of the mean and standard deviation of these variables.

Then calculating the composite weight of three variable by the given formula,

The composite weight of each district has been calculated by using this formula. The next step is to check out the reliability of W (Table 2). The table shows that the mean is 5.435 and std. the error of the mean is .06. Skew-ness can be quantified to define the extent to which a distribution differs from a normal distribution. Here, skewness is -1.028 which refers negatively skewed. That means the amount of higher value is higher and smaller value are fewer and the mean is less than the mode. Here, kurtosis is a measure of whether the data is heavy-tailed or light tail relative to a normal distribution. The value of kurtosis is 1.670, which refers data sets with low kurtosis tend to have light tails or lack of outliers. The next step is to determine the no of class by the formula (2^k = N). Where N=64 and no of class 6 is required. The 64 districts are divided into six classes based on the class interval method then, choose the best suits.

Equal Interval Method

Where, Highest value = B, Lowest value= A, Number of class requirement=6 (Figure 1) and (Table 3).

Table 2: Statistics of W.

Table 3: Frequency distribution of W in the equal class method.

Figure 1: Histograms of Equal Class Interval.

Mean SD Method: In this method using standard deviation and mean value in Figure 2. Here, mean is used as middle value and add 1SD, 2SD……Highest value and subtracting 1SD, 2SD……Lowest value (Figure 3) and (Table 4).

Arithmetic Method: A+X+2X…………...+NX=B

Figure 2: In this method using standard deviation and mean value.

Figure 3: Histogram of Mean SD Method.

Table 4: Frequency distribution of W in mean SD method.

Where, A= lowest value, B=Highest value, X= class interval, K= No of Class

The class interval is calculated as,

[A-(A+X)], [(A+X)-(A+X+2X)]…………………………………

Comparing the three histograms equal class interval method has a more symmetrical shape (Figure 4 ) and (Table 5).

Figure 4: Arithmetic Mean Method.

Table 5: Arithmetic method frequency distribution of W.

Data Interpretation and Results

Total 64 districts of Bangladesh grouped into six categories on the basis of three factors (Boro production, fisheries production and a number of growth center). These six categories have been re-grouped into three categories; highly productive, moderately productive, and low productive regions (Figure 5 ) and ( Table 6).

Figure 5: Agro productivity and Growth center Map of Bangladesh.

Table 6: Formal regionalization based on productivity for Bangladesh.

Agriculturally Low Productive Region

Among 64 districts, 10 districts of Bangladesh show the lowest production of rice, fisheries production and capability of trading. There are several reasons that are why the regions show the lowest production. One of the main reason is the natural disasters (hurricane, typhoon, cyclone) etc. Due to the yearly natural disasters in Barguna, Patuakhali, and Jhalkhati, the productivity is very low than the other districts (Table 6). This natural disaster creates a negative impact on agriculture. Another reason is the hilly areas. Bandarban, Khagrachori, Rangamati are the hilly areas in Bangladesh. Area of this region is 13,295 sq. Km. the physical condition of this area consists of earthen and hills rocks, waterfalls, river valleys, and forests [10]. Biswas and his fellow author seek out 1, 52,436 ha of total cultivate land and single cropped is dominant in this region. They also explore that cropping intensity is only 140% and due to lack of irrigation facilities 67,191 ha area remains fallow. Comparing this three hilly region Bandarban is one of the most disadvantaged and vulnerable regions in terms of various development indicators (income, employment, poverty, health and water, environment and sanitation (WES), education, inter-community confidence, etc.). Here the main disaster risk is landslide (24.67%). People are facing this risk for several years. Besides this 44.67% flood, 18.67% cyclone and flash flood 10.66% [11]. Due to the probability of this type of disasters, people are often prevented from the cultivation of the hill slope. Therefore, hilly areas are not suitable for rice production. Furthermore, due to the lack of growth Centre, lack of infrastructure facilities, low investment rate, adverse geo-climate conditions and low levels of urbanization and industrialization in this area, these regions shows the lowest productivity.

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Lupine Publishers| Comparison of Non-Destructive and Destructive Testing on Concrete: A Review

 Lupine Publishers| Journal of Civil Engineering and its Architecture

Abstract

Concrete is the oldest and most important construction material in the world. Testing of the concrete specimen plays and important role to know about the strength, durability and condition of the structure. The work will present a detailed comparison between the destructive tests and non-destructive methods. This work focuses on comparing the destructive and non-destructive testing which can determine the potential durability of the concrete. This work helped us to reach a conclusion where we can further find the best testing method system that shall be applicable for various concrete structures as well as in the concrete industry.

Keywords: Concrete; Compressive Strength; Destructive Testing; Non-Destructive Testing; Strength

Introduction

Concrete is the oldest and most commonly used construction material in the world, because of its durability, low cost and high availability Hassan [1]. It provides the most cost effective and efficient means of construction. Testing of concrete ranges from non-destructive where there the concrete specimen is not damaged to destructive testing where the concrete specimen might be slightly or completely damaged. 2 billion tons of concrete was produced in the year 2004 in the world, with India contributing 116.1 million tonnes Bhatacharjee, [2]. In today’s world concrete is made using various kinds of cement, coarse/fine aggregates, water, and admixtures if any. Proper infrastructure is one of the biggest drawbacks that halt the growth in India. The 12th five-year plan laid a special focus on the growth of infrastructure in India i.e. roads, highways, railways, communication and ports. One trillion is being invested in this sector during the 12th year plan. The world views India as a capable nation which is expected to show a growth from 1.2-1.5 billion by 2040 surpassing China which is already leading as the most popularly grown nation Rai and Ghavate [3]. A recent global report “Global Construction 2020” estimated India to be the third largest global construction market after USA and China. Today, the enhancement in the design capacity in India has reached a level where it is possible to design concrete with strengths of more than 100 MPa which wasn’t possible earlier. China has already used concrete strength up to 80MPa for high rise building construction within the cement usage set by the code standards Chatterjee [4].

The destructive testing method is suitable and economically beneficial for the concrete specimens that are produced at a large scale. The main aim is to investigate the service life and detect the weakness of design which might not show under normal working conditions. It includes methods where the concrete specimen is broken so as to determine mechanical properties i.e. hardness and strength. This type of testing is very easy to carry out, easier to interpret and yields more information. Some popular destructive test methods are as follows Shankar and Joshi [5]:

I. Tests of mechanical properties using the universal testing machine (UTM):

a) Tensile testing.

b) Bending testing

c) Compressive testing

II. Hardness testing.

a) Brinell test

b) Rockwell test

III. Impact testing

a) Pendulum test

b) Drop weight test

Destructive testing includes mechanical testing (bending, impact tests, tensile), macro/microhardness testing as well as metallographic examination. The various advantages of destructive testing are listed below:

A. Tests are economical and can be performed at a cheaper rate.

B. Equipment cost for destructive testing is cheap as compared to non-destructive testing.

C. It identifies mechanical properties (fracture strength, elongation, and modulus of elasticity)

D. It helps to reduce failures, accidents, and costs.

E. It helps in verifying the properties of the material Shankar and Joshi [5].

The various disadvantages of destructive testing are:

a. The internal defects of the concrete i.e. bubble, pores etc. can’t be determined.

b. The concrete specimens cannot be used again after the testing.

c. It cannot be used to detect early age deformities in concrete Kumavat et al. [6].

Non-destructive testing (NDT) is mainly concerned with the evaluation of flaws in materials which are in the form of cracks and which might lead to loss of strength in a concrete structure (Samson et al. [7]. NDT is a method for the testing of existing concrete structures so as to determine the durability and strength. In the modern construction world, it has become a vital part of the quality control process. NDT also helps in investigating about the crack depth, deterioration and microcracks present in concrete. Large no of parameters like density, strength and surface hardness can be determined by using NDT methods. It is also possible to check the integrity of structure and quality of workmanship by detecting cracks and voids Kumavat et al. [6]. It is applicable on both new as well as existing structures. Various NDT methods used in the field are as follows:

i. Rebound hammer test

ii. Ultrasonic pulse velocity test

iii. Combined ultraviolet and rebound hammer test

iv. Core extraction test

v. Ingredient analysis test.

The main aim of NDT is to assess one or more of in situ strength properties i.e. density, durability, and moisture content. NDT is the only way to assess the depth of cracks and to investigate whether any structural damage has occurred. Structural health monitoring by NDT like rebound hammer and UPV becomes very useful for the prediction of the service life of structure (Hannachi and Nacer, 2012). Experimental investigations determine that a good correlation exists between rebound hammer, UPV, and compressive strength. Rebound hammer test can be used alone to determine the compressive strength of concrete. UPV is an ideal NDT method to predict the deterioration of structures and the service life of structures. NDT has a vital role in everyday life and is very important to ensure reliability and safety. The main advantages of non-destructive testing are listed below:

I. The probe test generates variable results and provides the fastest means of checking maturity and quality of concrete.

II. Schmidt hammer test provides a simple, quick and inexpensive method of obtaining the indication of the strength of concrete with an accuracy of 15 to 20%.

III. Pull-out tests give information on development and maturity

IV. UPV method is the most ideal tool for determining whether concrete is uniform or not.

V. Radioactive equipment testing is very simple, and the running cost is less, although the initial price might be very high.

The main disadvantages of non-destructive testing are:

A. Interpretation of results is difficult.

B. The manual operation requires experienced and skilled technicians.

C. It is difficult to inspect the concrete specimens that are irregular and full of voids Kumavat et al. [6].

Literature Review

Figure 1: Compressive strength vs velocity of concrete specimens Lopez et al. [8].

Kumavat et al. [6] carried out an experimental study on combined methods of NDT in concrete and evaluation of core specimen from existing buildings. Ultra-pulse velocity rebound hammer and core tests were carried out on the specimens according to IS standards and combining the two methods. Regression analysis was carried out and correlation coefficients were given. Charts were plotted between rebound numbers, UPV against the compressive strength of the core specimen. The comparison showed that use of combined methods gives higher efficiency on estimation of concrete compressive strength. The results obtained gave a correlation coefficient of 0.003 and 0.355 for rebound value and UPV value. A higher correlation coefficient of 0.441 was obtained when two methods were combined. Lopez et al. [8] experimentally studied the concrete compressive strength estimation by NDT. The main aim was to produce a correlation between results of surface hardness, UPV and compressive strength of structural concrete in bleachers of a soccer stadium in Parana, Brazil. The concrete structure used in the study was 26 years old and had some severe deformities i.e. segregation, corrosion, and cracks. Mapping reinforcement was performed and UPV test was done according to the IS standards. 26 specimens of concrete were collected and correlation curves between NDT results were plotted. The results showed that stronger the concrete, higher shall be its surface index as well as its wave propagation velocity. Results also showed a good correlation between both surface hardness test and UPV test (Figure 1).

Bhosale and Salunkhe [9] experimentally found the relation between destructive and non-destructive tests on concrete. Different concrete mixes of M20, M25, and M30 were used and a slab of 2000*1000*200 mm was casted for each grade and cores were extracted from the slab. Cylinders of size 100*200mm, Cubes of size 150*150*150mm and cubes of 150*150*150mm with an inserted bar of size 16mm were cast. Casted cubes after 28 days were tested to obtain compressive strength using CTM. Rebound hammer test was performed and an average of 12 readings was taken. Regression analysis was done, and various correlations were achieved which are given as follows:

1) The relation between the compressive strength of cylinders (f cyl) and cores (F cor)

F cor = -0.034 f cyl2+ 2.586 f cyl -19.25

2) Relation between rebound strength of cylinders (R cyl) and cores (R cor)

R cor= -0.020 Rcyl2+2.15 R cyl -16.75

3) Relation between rebound ultra-pulse velocity of cylinders (U cyl) and cores (U cor)

U cor= 1.373 U cyl2+ 12.18 U cyl -22.95

4) Relation between rebound strength (R cor) and UPV strength of cores (f cor)

R cor= -0.050 f cor2 + 3.987 f cor – 31.16

5) Relation between UPV (U cor) and compressive strength (f cor) of cores

U cor= -0.003 f cor2+ 0.18 f cor +1.410

6) Relation between rebound strength and UPV of cores

U cor= -0.002 R cor2 +0.166 R cor + 1.671

7) Relation between rebound strength and compressive strength of cylinders

R cyl = -0.037 f cyl2 + 2.712 f cyl -19.85

8) Relation between UPV and compressive strength of cylinders

U cyl= 0.0222 f cyl + 3.64

9) Relation between rebound strength and UPV

U cyl= 0.001 R cyl2-0.052 R cyl + 4.355

Figure 2: Compressive strength vs. cube no at 7, 14 and 28 days Patil et al. [10].

Patil et al. [10] deduced the comparative study of the effect of curing on strength of concrete using DT and NDT methods. 27 cubes of M25 grade were casted and allowed to be cured for 7, 14 and 28 days and rebound hammer test and compressive strength test was performed on 9 cubes of 7, 14 and 28 days respectively. The results showed that the rebound number increased as the compressive strength increased and vice-versa. For 28 days of curing decrease in percentage, strength was less as compared to 7 days percentage decrease in strength and average error in measuring compressive strength for 7, 14 and 28 days by rebound hammer and CTM was found out to be 20.01%, 1.37%, and 0.99% respectively. Results also showed that compressive strength or rebound number could be produced if only one of the values was known (Figure 2).

Balwaik [11] experimentally compared the direct, semi-direct and indirect method of testing. A randomly selected school building was taken and a complete analysis of all the structural members was carried out using the direct method of testing. Various defects like air gaps, hollow spaces and voids were identified and all the structural members were grouted at junction points so as to avoid collapsing of members. Results showed that direct UPV method was found to be reliable in detecting of the flaws as compared to indirect and semi-direct methods of testing. Damodar and Gupta (2014) experimentally investigated to develop an ideal curve equation for early prediction of concrete’s compressive strength. OPC, PPC and PSC cement were used in the experimental work.18 cubes of the 1st batch of M20, M25, and M30 grade were cast and subjected to normal curing. 3 cubes from every mix were tested for compressive strength at 1 and 3 days respectively and the result of an average of 3 cubes was taken. Results obtained from the experiment showed that OPC gained strength of 80% in the 1st day of accelerated curing while as PSC and PPC only gained 50% strength in the 1st day and these results could be used in future for prediction of the early strength of concrete. Results also showed that an ideal curve equation could be obtained and used in computing the compressive strength of concrete (Table 1). The gain in compressive strength is given by: y= (ab) x

Table 1: Compressive strength comparison of Mix M20, M25 and M30 in MPa (Damodar and Gupta, 2014).

Where, y represents compressive strength, a represents factor comprising parameters of various design mixes, b represents the coefficient of no of days the system has been subjected to curing and x represents no of days the cubes which are subjected to curing.

Savaliya et al. [12] studied the effect of age on mortar and concrete specimens through an experimental program. 6 concrete and mortar beams of size (150x150x700mm) and 6 concrete and mortar cubes of size (150x150x150 mm) were cast and subjected to direct, indirect and semi-direct UPV testing at 7, 28 and 56 days respectively. Results showed various relations between velocities of UPV, the age of mortar and concrete. The relation between velocity and age of concrete, where y represents the ultra-pulse velocity and x represents the age of concrete

y = 0.0244 ln (x) + 4.6277

The relation between velocity and age of mortar, where y represents the ultra-pulse velocity and x represents the age of mortar.

y = 0.1132 ln (x) + 3.2871

The results also showed that velocities measured by keeping the transducers on the bottom and top surfaces in semi-direct UPV testing gave different results. The relation between age of concrete and velocity of transducers on the top surface, where y represents the velocity and x represents the age of concrete.

y = 0.1051 ln (x) + 4.7836

The relation between age of concrete and velocity of transducers on the bottom surface, where y represents the velocity and x represents the age of concrete

y = 0.0469 ln (x) + 5.0426

Nacer and Hannachi [13] investigated the application of the combined method of UPV and RH tests for calculation of compressive strength. UPV and RH tests were measured with mechanical tests done on cylindrical specimens. The tests were used to arbitrate quality of concrete using regression analysis modes. Equations were obtained by statistical analysis to analyses concrete’s compressive strength on site. Correlation charts were plotted, and regression equations were listed (Table 2). The results showed that using more than one NDT provided a better correlation and lead to predictable evaluation of concrete’s strength. The results also showed that combined methods appeared more appropriate on conditions of on-site measurements as they were very fast, convenient and cost efficient. Shang et al. [14] found the strength of concrete using NDT methods using experimental study. All the samples were made from locally available materials and were confirmed to Chinese standard (GB 175-2007). Five sets of M20, M25. M30, M40, and M50 mixes were prepared and each containing 21 concrete cube specimens of the size (150x150x150mm). Rebound hammer test was performed on the specimens and 16 readings were taken for each specimen. Regression analysis was done, and curves were drawn for the rebound hammer method. Results showed that the rebound hammer was found reliable in predicting the early strength of concrete. It was concluded that regression models for the assessment of strength could be used for prediction of concrete strength (Table 3). Shariati et al. [15] assessed the strength of RC structures through UPV and rebound hammer tests and an interrelationship between DT and NDT tests was established. Main members of an existing building including a column, beam, and slab were tested by NDT. Regression analysis was done, and calibration curves were drawn. Correlation between predicted and actual compressive strength of concrete was interpreted by plotting average rebound no/ultrasonic pulse velocity against the compressive strength of each member. Results obtained from the experimental study showed that the regression model achieved from the combination of two NDT methods was more precise as compared to the individual methods. Results also showed that the rebound number method was more effective in forecasting the compressive strength of concrete than the UPV test method. The best-fit curve that represents the relationship for UPV results has the following equation:

Table 2: Regression equations for Cylindrical and core Specimens (Hannachi and Nacer, 2012).

Table 3: Rebound Curve for Concrete measurement and error (Shang et al., 2012).

fc (V) = 15.533V - 34.358

Where V is the ultrasonic pulse velocity. The best fit curve that represents the relationship for the combined method has the following equation:

fc (V) = -173.04+4.07V2+57.96V+1.31R

Where V is the ultrasonic pulse velocity and R is the rebound number.

Aydin and Saribiyik [16] carried out an experimental investigation to develop a relationship and correlation between rebound hammer test (NDT) and compression test (DT). Cube specimens of size 15*15*15cm and a no. of core samples from different RC structures were tested. Rebound hammer test and the compressive test was performed on the specimens. The curves were drawn and the best fit correction factors for concrete compressive strength were obtained through processing the correlation among the datasets. The results drawn from the investigation showed that use of rebound hammer test on existing buildings was not found suitable for evaluation of strength in old structures of concrete. Results also revealed that rebound hammer tests could be used alone as a reliable means to estimate the strength of concrete specimens if the needed calibrations were done (Table 4).

Table 4: .Regression outputs for 28 and 90 days concrete specimens (Aydin and Saribiyik, 2010).

Turgut and Kucuk [17] carried out an experimental study to compare direct, indirect and semi-direct UPV testing on 30 concrete blocks of size (30x30x25cm) at 28 days. 6 locations were taken in each measurement for each concrete block with path lengths of 250, 150, and 195 for direct, indirect, and semi-direct testing respectively. Results showed that average direct UPV was 9% higher than indirect and semi-direct UPV in concrete blocks. Results also showed that direction of casting in concrete affected UPV. It was found out that UPV was less in concrete casting direction than in horizontal direction. The regression analysis was carried out and best fit lines representing the relationships have been summarized in Table 5.

Table 5: Correlations between UPV measurements (Turgut and Kucuk, 2006).

Conclusion

It has been seen from the literatures reviewed that both the destructive and non-destructive tests help in assessing the strength of concrete. At times where the destructive tests on concrete cannot be employed, one prefers to utilize the non-destructive tests. NDT has a vital role in everyday life and is very important to ensure reliability and safety. A number of advantages were discussed for the various tests that are a part of NDT. The researchers at various instances found that the combination of the NDT tests proves to be more accurate and beneficial than one of the tests alone. The results drawn from the investigations also showed that use of rebound hammer test on existing buildings was not found suitable for evaluation of strength in old structures of concrete and rebound test was useful in finding the early strength of concrete. Results revealed that It was concluded by various researchers that regression models for the assessment of strength could be used for prediction of concrete strength. Thus, it is concluded that using more than one NDT provides a better correlation and lead to predictable evaluation of concrete’s strength. The results also revealed that combined methods appeared more appropriate on conditions of on-site measurements as they were very fast, convenient and cost-efficient.

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Lupine Publishers| Physico-Mechanical Properties of Plaster Mortar Reinforced with Date Palm Fibers

 Lupine Publishers| Journal of Civil Engineering and its Architecture

Abstract

The aim of this study is the use of local materials (plaster, sand dunes and date palm fiber) for the region of southern Algeria. By expand areas of the use of these materials in the field of construction. Despite the large ament of gypsum, its use is limited to some secondary operations like coatings and decorative elements. The sand dunes and palm fiber, its use in the construction are very limited. In this study, the sand dunes and palm fiber was added to plaster, to find the mortar that has physical and mechanical properties that allow its use in construction. The results obtained showed that the addition of date palm fibers improves the physical properties (density, water absorption, etc.) and mechanical properties (compression strength, flexural strength, etc.).

Introduction

The Algeria, especially the South, is rich in natural materials, which can then be used directly in the construction field he must study their properties in order to extend their use. Among these materials, which can be exploited, and that we will consider, plaster, sand dune, and the fibers of the Palm. The use of vegetable fibers in the reinforcement of building materials to improve certain properties, it is the most used technology currently, because these results and to expand the use of eco-materials. Algeria has unlimited sources of vegetable fibers (of Palm, Alfa Abaca, hemp, Cotton,), but their use in the construction of the almost non-existent field. The incorporation of the fibers of date palm in the mortar of plaster, is carried out in order to improve the tensile strength and decrease its fragility. The major assumption that the fibers allow the judgment of the cracking mechanism, delaying the start of the crack and the controlling once it appears. In our study, we will examine the effect of the addition of fibers of palm trees date palm to the physical and mechanical properties of the Mortar plaster. Where we are looking at the impact of the rate and length of the fibers of date palm on the characteristics of mortar plaster, in the short and in the long term.

Materials used

The Materials used are those available at the local level:

Sand Dunes used: In our study we used the sand dunes of Guerrera (GHARDAIA). The physical properties of sand dunes used are represented in Table 1.

Mixing water: The used mixing water is the public drinking water of the network of the city of Ghardaia.

Lime: Air lime as a retardant of setting time of the plaster was used, because it decreases the solubility of the latter and allows to increase the time of employment. In addition it does not affect these mechanical properties. A chemical analysis of the lime used was performed using the method of diffractometer by X-rays in the lab. Physics at the University of Laghouat, the results of this technique are presented on the diffractogram me below [1] (Figure 1).

Figure 1: Diffractogramme of the powder lime by X-ray.

Fibers: The fibers used are vegetable fibers of DOKAR of date palm in the region of Ouargla. The Spectrochemical Analysis of the powder of the fibers after calcination at 400°C gave the following elements [2]. The fibers used with the following characteristics [3] (Tables 2 & 3)

Table 1: The physical properties of sand dunes

Table 2: Chemical analysis of the powder of fibers calcined at 400°C

Table 3: Physical and mechanical properties of the fibers used.

Plaster: The used plaster is a local product taken from the career of oasis in Ghardaia. It is available in the market. The chemical analysis is summarized in the Table 4. We can summarize certain essential properties in the Table 5, to identify the plaster (Table 5).

Table 4: Chemical analysis of plaster.

Table 5: Essential Properties of plaster.

Formulation of Plaster Mortar with Fiber: The determination of the composition of mortar plaster reinforced with fibers of date palm, we used the same composition with the classic mortar, so we take the following composition:

I. We take the report E/(P+S) = 0.6.

II. The report of S/P is set to the value 0.5.

III. They add 6 % limes air as retarding of setting time.

IV. After the preparation of fibers of date palm, we respect the recommandations of Kriker [2], for this, the fibers used are treated in the water, then dried in the free area.

V. The mixing is carried out in the following way.

VI. We are mixing first of all the Sand and fibers to sec.

VII. The plaster is added, while blending it well with the sand and fibers.

VIII. It adds the mixing water and lime and malaxant well the mixture.

Confections of Samples and Storage Conditions: After the mixing, it fulfils the mussels to reason of two layers and vibrate the mortar using a rod to ensure a good distribution and a proper orientation of the fibers, and finally grind and smooth the surface of the mortar. The test pieces are assembled, they are placed in the open air in the laboratory. After 24 hours, these are removed and placed in free air at a temperature of (25°C±1°C) up to the time of the test, this procedure is made for all the compositions and for all tests.

the samples used are (4x4x16)cm3 for the following tests.

i. Determining the density.

ii. Absorption of water.

iii. Tensile strength.

iv. Compression strength.

Composition of mortar of plaster reinforced by fibers of date palm: To get a good composition of mortar plaster reinforced with fibers of date palms, we follow the following steps:

First of all, we use the same composition of pate of mortar base of plaster, which we have obtained in the step above.

a. As regards the fibers we tried to determine.

b. First of all the mass fraction optimal fiber to introduce in the mortar of plaster using the fibers of the date palm to a constant length L=10mm and by increasing the dosage of fiber from 0% to 2% with a step of 0,5% by mass.

c. And then, the optimal length for the optimal fraction that we found previous for each length, 10mm, 20mm, 30mm, et 40mm.

Laying all tests, that we were conducting, keep well the workability of dough into court of sitting time. Because the addition of plant fibers to a mineral matrix leads to a decrease in workability.

All the samples are retained in the ambient air of the laboratory until the age of 14 days.

Results and Discussions

Variation of Physical And Mechanical Properties of The Mortar Plaster Reinforced by Fibers of Length of 10mm with Different Percentages

The results of the variation of physical and mechanical properties of the Mortar plaster reinforced by various dosage of fiber are:

A. The density : From Figure 2, we notice that density decreases slightly with increasing the dosage of fiber, which can be explained by the increase in the volume of void created by the incorporation of fibers where obtaining a less dense plaster mortar. This result is in agreement with the research of DJOUDI [1].

Figure 2: Variation of density of mortar of plaster in function of the percentage by mass of fibers.

B. The absorption of water: Figure 3 illustrates the evolution of absorption of water for a mortar of plaster reinforced with fibers of a date palm, it is clearly visible that the absorption of water increases according to the increase in the percentage of the fiber plant, this is due to the volume of the high vacuum created by the addition of the fibers and by the nature of the fibers themselves. These results correspond to the results obtained by DJOUDI [1] in his research on concrete plaster reinforced with fiber of date palm, it has been found that incorporation of fibers increases the water absorption of concrete plaster

Figure 3: Variation of water absorption of mortar of plaster in function of the percentage by mass of fibers.

C. Compression strength: According to Figure 4, it can be seen that between 0% and 1% a slight increase in the compressive strength, then 1,5% an acute increase in the compressive strength and after this percentage a Fall in compressive strength. the increase in the compressive strength of mortar, plaster reinforced by fiber of the palm, from the non fibré mortar can be explained that the fibers in the percentage of fat play a role in normal concrete aggregate, and the fall that occurred after this increase, we can judge that the addition of fiber disruption the mortar with mineral skeleton void inside the dough and increasing its porosity, with minimal resistance. These findings are in agreement with most of the research conducted, as Kriker [2], in its research on the concrete reinforced by fibers of palm.

Figure 4: variation of compressive strength of mortar cast according to the mass percentage of fibers.

Figure 5: Variation of the flexural strength of plaster mortar as a function of the percentage by mass of fibers.

D. The flexural strength: Figure 5 shows the influence of the length of the fibers on the flexural strength of fiber mortar. First of all, we note clearly that the flexural strength considerable increases with all the lengths of the fibers. A net improvement for the fibers of lengths of 10mm and the resistance reaches the maximum for the lengths of 20mm. After, a decrease in the resistance for lengths 30mm and 40mm, which can be always translates by the loss of manoeuvrability that due to a exercised of fiber and a poor distribution of fibers in the pate increasing porosity and consequently a decrease in the flexural strength. By simulation, we find that the mortar of the plaster has the same properties of the cement mortar. That appears in the research on the cement mortar reinforced by strip of wood. It was found that, for a mortar to 2% had a flexural strength that 3/10 mortar witness that is to say three times more.

E. Recapitulation: The fibers of length 20mm give the best results of resistance to compression and flexion. As these fibers give acceptable results in the density and absorption of water. As for the handling, the mortars reinforced by the fibers of length of 20mm have a good workability and facilitates the implementation.

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