Properties of Concrete as Influenced by Shape and Texture of Fine Aggregate

Shape and texture of aggregate is one of the major parameter that influence the properties of fresh and hardened state of concrete. The present methods on mix proportioning of normal concrete have incorporated shape characteristics of aggregate. Since the classification of aggregates is very broad. It often leads to inconsistent results and the property of concrete varies. Thus quantification of these properties is essential to further rationalize the process of concrete mix proportioning. Various codes have envisaged certain tests that indicate the shape characteristics of aggregate. Flakiness index, Elongation index and angularity number, Index of aggregates particle shape and texture (IAPST). An elaborate study covering fine aggregates with different size, grading, shape and texture characteristics is essential. However, this paper deals with the study of the influence of shape and texture of fine aggregate (natural sand, stone dust) on concrete mix proportioning. Experimental investigation was done on fine aggregate with different shape and texture characteristics, water cement ratio, water content, and coarse aggregate content for the study. Aggregate of 10 mm and 20 mm from single source as coarse aggregate and 53 grade (28 days strength of 53 Mpa) ordinary Portland cement are considered as the constant parameters.


Introduction
Advances in the development of concrete for intended use are going at a faster rate. The list of different types of concrete, each suitable for a specific, is lengthy. Some of the types worth mentioning are, structural lightweight concrete, heavy weight concrete in its entirely as a construction material is gaining popularity. This concept is symbolized with the increasing use of ready mixed concrete (RMC). The focus of the research has now shifted from mere strength as criteria in the yester years to performance of concrete. Modern concrete need to comply performance attributes such as high strength, high modulus of elasticity, high density, low permeability, improved resistance to cracking, better ductility, improvement in bond with steel, etc. High Performance Concrete (HPC) and Self Compacted Concrete (SCC) are the major developments in this regard. High strength and low permeability are the essential features of HPC. Unlike normal strength concrete the three phases, namely, aggregate, hydrated cement paste and interfacial zone are pushed to their limiting strength in case of HPC. As the strength of hydrated cement paste is, in general, more than that of aggregate hence the strength of aggregate limits the strength of concrete. It is observed that no standard procedure is available for the selection of proportions of materials for HPC. However, methods proposed by different researchers can be used as guideline for arriving at trial mix of HPC P. K. Mehta et. al, and B. H. Bharatkumar et. al and F. de Larrard et. al. The use of different types of cements, mineral and chemical admixtures has also been suggested. The limit of maximum cement content to 450 kg/m 3 will boost the utilization of mineral admixtures such as fly ash, silica fume, rice husk ash, metakaolin, ground granulated blast furnace slag etc. and prevent the concrete from the hazards of higher cement content. Concrete is a composite consisting of binder and filler materials. The binding medium in the case of hydraulic cement concrete is the paste of cement. Aggregates act as filler material. The mixture gets hardened with age giving strength and volume stability to the concrete. The properties of concrete are influenced by the properties of its ingredients and their relative proportions. Major contributors to the properties of concrete. Shape is another property, which has a major influence on properties of concrete. It is broadly described as angular, rounded, flaky and elongated. Angularity indicates sharpness of edges and corners M. F. Kaplan studied the effect of various properties of coarse aggregates on workability of concrete. The properties included were flakiness index, elongation index, angularity number, surface texture, moisture content and crushed aggregates and also by crushing the aggregates with low to high reduction ratios. Thirteen coarse aggregates were considered in the investigation. For each coarse aggregate, flakiness index and elongation index, angularity number as suggested by Shergold surface texture as suggested by Wright water absorption and moisture content as per the drying method was determined. River sand from single source and ordinary Portland cement from single batch was used in the investigation. Three mixes with each coarse aggregate were cast with different w/c ratio, aggregate cement ratio and type grading as per Road Note No.4. Compacting factor and veebe tests were conducted to assess workability of concrete. Three tests on different days were carried out and the average of test results reported. It was expressed that the reproducibility of results of compacting factor test was more than veebe test. It was shown that the angularity number of aggregate has greater effect on workability of concrete than other indices. Highly angular particles require more water for their wetting but may provide better interlocking. Rounded aggregate contain fewer voids, which result into higher workability than angular aggregates for the same water content. Flaky and elongated particles have detrimental effect on durability of concrete. M. Shabbir Hossain, Frazier Parker and Prithvi Kandhal presented data of different tests conducted on various type and sizes of coarse aggregate. The tests included fractured particles as per ASTM D 5821, flat and/or elongated particles as per ASTM D 4791, IAPST as per ASTM D3398 and uncompacted void content as per modified ASTM C1252 as proposed by Ahlrich. All the tests were performed on single sized particles, namely, 19-12.5mm, 12.5-9.5mm, and 9.5-4.75mm. In case of fractured particles tests, percentages for "one or more" fractured faces and " Two or more" fractured faces is defined as that face which has a projected area at least one quarter of the maximum projected area (maximum cross sectional area) of the particle with sharp and welldefined edges. Authors observed that the measurement of fractured face count is not precise. In case of flat and/or elongated particles test, percent of particles with width to thickness and length to width ratio 3: 1 and 5: 1 respectively, were measured on both mass and particle count basis. IAPST test as per ASTM D3398 was conducted. Uncompacted void content of coarse aggregate particles was determined as per method B of ASTM C1252 but with modified device suitable for coarse aggregate size fraction. Based on the results it was concluded that, ASTM D3398 and uncompacted void content provide a measure of coarse aggregate particle shape, angularity and surface texture. These methods were reported as more objective and precise than other methods. However, it was expressed that for the use of these methods as a specification, the criteria for flat and/or elongated particles should also be included. B. P. Hudson discussed about the production of manufactured sand and the influence of type of crushing equipment, reduction ration, etc. on the shape characteristics of aggregate particles. The author reported that impact crushers are superior to compression type crushers (Jaw crusher). Autogeneous vertical shaft impactors produce particles of good shape as the particle undergo impact and abrasion during their crushing to smaller size which is similar to the process by which natural aggregates are formed. Cubical particles are most abundant in the size range near to crusher setting. Jaw crushers are not able to produce a good particle shape in the size range of 2.36mm to 300 micron, as it is not possible to set the side setting of crusher to 2mm. in case of cone crushers choke feeding should be employed. It was expressed that low reduction ratios are favorable while crushing. Shergold suggested a method for determining angularity of aggregate based on the principle of voids. The method consisted of separating the aggregate sample in to closer size fractions. Aggregate from each size fraction is compacted in three layers. Each layer is compacted by applying 100 blows of standard tamping rod at the rate of 2 blows per second and distributed uniformly over the surface of aggregate. Each blow is applied from a height of 50 mm above the surface of aggregate. After finishing compaction of all the layers the mould is filled to overflowing and then excess material is striked off. The mass of the aggregate in cylinder is measured. The test is repeated three times using the same sample and the average value of weight of aggregate is considered for the determination voids in the aggregate sample. Author found that the percentage voids in well-rounded gravel, when compacted in the similar manner as 33, which was taken as reference. Following equation was proposed for determining angularity number of the aggregate size fraction.
Angular Number=Percentage Voids-33 Weighted average of angularity number of different size fractions in a given sample is considered as the angularity number of aggregate.
However, it was expressed that the method cannot be applied for regular shaped bodies. The aggregate by Indian and British standards (IS 2386 -1963 Part-I, BS 812-1975) Author reported that the angularity number might vary from 0 for well-rounded gravel to 12 for very angular crushed rock. The angularity number of about 100 samples of aggregate reported to have shown good agreement with visual identification. Author has also presented the results of compacting factor test conducted on concrete mixes incorporating coarse aggregate s having different angularity number. It was shown that good correlation exit is a pioneering work in the measurement of angularity of aggregate. Though the method provides a measure of aggregate angularity, it has some shaped bodies such as sphere, cube, etc. Furthermore heavy compaction involved in the process may break the aggregates, change the surface characteristics and thereby cause artificial changes in angularity M. C. Nataraja, et al Surface texture of aggregate is also an important property which influences bond between the aggregate surface and cement paste and thereby mechanical properties of concrete. L. K. Crouch and Roy C. Lotzenheiser investigated the influence of coarse aggregate angularity and surface texture on the compressive strength of high strength plain cement concrete. Rounded river gravel from single source and of the size 9.5mm to 2.36mm with constant grading confirming to ASTM C33 was used. Gravel was crushed to produce crushed aggregate. Concrete mix was produced with 10 each using rounded aggregate, crushed aggregate and equal amount of each shape. Device used in ASTM C1252 was up scaled to suit the measurement of uncompacted void content of each coarse aggregate. Compressive strength tests were conducted at 7, 28 and 56 days using 100 X 200mm cylinders for every batch. Liner regression analysis was carried out to establish the relationship between compressive strength and uncompacted void content of coarse aggregate. High correlation coefficients of 0.98, 0.95 at 7, 28, 56 days respectively indicated the influence of shape of aggregate particle on strength of concrete. It was expressed that measurement of shape of aggregate is useful for pre-evaluation of aggregate for their use in high strength concrete. The paper presented by Randy C. Ahlrich focused on the influence of aggregate particle shape and texture on permanent deformation characteristics (rutting) of hot mixed asphalt (HMA) mixtures. Uncrushed obtain aggregate with variation in shape and texture characteristics. In all there were 11 aggregate blends. Each aggregate blend was separated on the 4.75mm sieve to allow characterization of coarse and fine aggregate fractions. Each fraction was tested for IAPST as per ASTM D 3398 and uncompacted voids content as per ASTM C 1252. The device used for fine aggregate in ASTM C 1252 was modified to suit the coarse aggregate fractions (20 to 4.75mm size). Dynamic creep test was conducted on the HMA mixtures for evaluating rutting potential. It was reported that IAPST as per ASTM D3398 and modified ASTM C1252 for coarse aggregate and ASTM C1252 test for fine aggregate effectively characterized the shape and texture of aggregate blends. Generally crushed particles will have rough surface texture and hence they provide better bond than the rounded aggregate. Hence objective quantification of aggregate properties is essential for the better control over the properties of resulting concrete. Wright proposed a method for the quantification of the surface texture of aggregate particles. It consisted of embedding aggregate particle in synthetic resin and obtaining thin sections of aggregate surrounded by the resin once the resin hardened. The interface between stone and resin was magnified 125 times on a projection microscope and traced. The length of the profile was measured by means of map-measuring wheel and compared with the length of an unevenness line drawn as a series of chords. The difference between two lengths was considered as the measure of roughness. Concrete should possess adequate workability and cohesiveness in the fresh state, strength and durability in the hardened state. The properties of ingredients such as strength, chemical composition, fineness and consistency of cement, size, grading, shape and surface texture of aggregates, quality of water, and type of mineral and chemical admixtures will have a bearing on the properties of concrete. Out of the different materials used in the making of concrete, there is a least control over the properties of aggregates. However, it is one of the major contributors to the properties of concrete. It occupies bulk of the volume, imparts volume stability and because it is cheaper than cement, it reduces the cost of concrete. It is well recognized that the aggregate is not simply a filler material but its physical, chemical and thermal properties of concrete in fresh and hardened state ACI 221R-89 Size and grading of aggregate influences workability, strength, shrinkage and unit weight.

Preliminary Investigations
Outline of Preliminary Investigation A broad objective of the experimental investigation is to study the role of shape and texture of aggregates in concrete mix proportioning. In this regard, the study of available methods for the quantification of these properties is a first step. It is understood from the literature that there are no precise methods for the quantification of shape and texture of aggregates. However, various codes have envisaged certain tests that indicate the shape characteristics of aggregates such as Flakiness Index, Elongation Index and Angularity Number Uncompacted Void content, Index of Aggregate Particle Shape and Texture (IAPST). Digital image processing techniques are also being attempted for the same. As ASTM C 1252 is meant for fine aggregates and digital image processing techniques are still in the development stage. IAPST test considered for preliminary investigations. Moreover, the preliminary investigation is aimed to carry out reconnaissance of aggregates available in the vicinity and study their shape and texture characteristics.
Procurement of Material Fine aggregates from different crushing plants, river sands from different sources have been considered in the investigation. All the aggregates were washed clean and dried. The aggregates were sieved in to closer size fractions by selecting 20mm, 10mm and 4.75mm sieves in case of coarse aggregates and 4.75, 2.36mm, 1.18, 600micron, 300micron sieves for fine aggregates. Each size fraction was stored separately Tests on Shape and Texture of Fine Aggregate Index of Aggregate Particle Shape and Texture (IAPST) The dimensions of the metal cylinder and tamping rod used in the test for various size fractions of the aggregate are given in Table 1. Test is conducted on each size fraction separately. A sample of aggregate size fraction to be tested was drawn using coning and quartering method of sampling. Mould and tamping rod appropriate for the size fraction of aggregate were used. The mould was placed on a level and solid base from vibrations. Mould was filled with aggregate to one-third of its height by gently poring aggregates from the scoop from a least possible height. Aggregate surface was gently leveled with the finger Layer was compacted by applying 10 drops of tamping rod uniformly distributed over the surface of aggregate. Each drop was applied by dropping the tamping rod freely from a height of 50mm above the surface of aggregate. The height of after the completion of tamping of second layer aggregate just sufficient to fill the mould and poured and compacted in a similar manner. Individual pieces of aggregate were then added and rolled till the surface of aggregate was level with top of mould. Weight of the aggregate in the mould was measured to an accuracy of 1gm. Repeat test was conducted on the same aggregate and average weight (M 10 ) was obtained. The process was repeated with 50 drops and average weight (M 50 ) was obtained. The percentage voids after 10 and 50 drops are calculated using following equations Where, V 10 -Percentage voids after 10 drops V 50 -Percentage voids after 50 drops S -Specific gravity of aggregate size fraction V -Volume of Cylinder in m 3 . IAPST is determined using following equation Weighted average of IAPST of individual size fractions was determined as per the percentage of weight of the size fraction in grading. The values of V10, V50 and IAPST of all the aggregates are presented in Table 2.

Experimental Programme
Outline of the Experimental Program Preliminary investigation has given good insight into the type of aggregates available in the vicinity and the parameters such as IAPST to characterize aggregates. The established characteristics of aggregates that influence proportioning are size, grading, shape and surface texture. They in turn influence strength and workability of concrete. Nominal maximum sizes of aggregates used in concrete are 10, 20, 40mm etc., out of which 20mm is widely used. Hence maximum size of the aggregate used in the experimental Programme is 20mm. The influence of grading of aggregate on properties of concrete is well recognized. Standard grading are prescribed by various codes for coarse and fine aggregate to be used in concrete. The influence of grading of fine aggregate is more than that of coarse aggregate. Hence in the present investigation on two fine aggregate grading (a grading each from Zone -II and III). River sand is most commonly used as fine aggregate. The reconnaissance of river sand and stone dust from various sources in the vicinity

Experimental Program with Shape and Surface Texture of Fine Aggregate as Variable
Water cement ratio is a major parameter that influences the strength of concrete. It is well known that for a given material, as the water cement ratio increases there is a reduction in strength. Subsequent research indicated that shape and surface texture characteristics of aggregates also influence the strength of concrete. Cohesiveness and workability is another important property that the concrete should possess. For given material and water cement ratio there exists a unique combination of coarse and fine aggregate that gives maximum workability for particular water content. Higher the water cement ratio higher is the fine aggregate content for a cohesive mix. In this present investigation M20

Properties of Materials Used in the Investigation
Cement OPC 53 grade of a particular brand was used throughout the work. The physical properties of cement such as standard consistency, initial and final setting time and 28 days compressive strength were tested and presented in Table-3. Cement was stored in thick plastic bags to avoid the formation of lumps.
Aggregates Coarse aggregate, river sand and stone dust from single source are used in the experimental work. Their properties namely, specific gravity in saturated surface dry condition, water absorption and bulk density are determined and presented in Table-4 and Table 5. While the indices of shape and texture namely, IAPST.
Water Potable water available in the laboratory was used.

Production and Tests on Concrete
Batching All the material was weigh batched as per the proportions of the mix. In case of aggregates, each size fraction was batched separately so as to obtain the required grading Mixing All the ingredients of concrete were thoroughly mixed. The mixing was carried out at a room temperature of 30 ± 2°C. The weight of the aggregate and quantity of water was adjusted as per the water absorption and status of surface moisture of aggregates.
Tests on Workability of Concrete Compacting factor test was conducted simultaneously on each mix. In the case of compacting factor test due care taken to release the concrete from upper hopper of the apparatus two minutes after the completion of mixing.
Test on Compressive Strength of Concrete 3 cubes of size 150 X 150 X 150 mm were cast each concrete mix, cured for 28 days in the water tank and tested under compression testing machine Test on Spilt Tensile Strength of Concrete 3 cylinders of size 150 mm diameter and 300mm height were cast each concrete mix, cured for 28 days in the water tank and tested under compression testing machine

Compressive Strength
In this Investigation, Compressive strength was found out for three grades of concrete. From the results, shown in Table-6 it is visible from the Figure 4 that compressive strength was increased with different shape and texture and varying IAPST values for zone -2 fine aggregate in M20 grade of concrete and decreased for M25 and M30 grade of concrete. The OPC samples showed slightly higher compressive strength when IAPST value increased. The influence of IAPST is reduced strength of M 25 and M30 grade of concrete. This was likely to decrease due to use of different shape and texture of aggregates. This was discussed earlier by L. K crouch et.al and for zone-3 fine aggregate, Compressive strength decreases with increase of IAPST values as shown in Figure 5.

Split Tensile Strength
In this Investigation, Split Tensile was found out for three grades of concrete. From the results, it is visible from the Figure 6 that there was gradual increase in split tensile strength for M20 M25 and M30 grade of concrete for Zone 2 and Zone 3 and it is observed that there is further decrease in strength with increase of IAPST values as shown in Figure 7. This was likely to be due to use of different shape and texture of fine aggregate.

Workability
It is observed that there is further decrease in work ability with increase of IAPST values in zone 2 and zone 3 as shown in Figure 8 and Figure 9. This was likely to be due to use of different shape and texture of fine aggregate.

Conclusions
In this study, the effect of IAPST on zone 2 and zone 3 fine aggregate on the mechanistic properties of concrete was examined. Replacement of the fine aggregate with different shape and texture led to a decrease of compressive strength and work ability compared with the conventional OPC concrete. The split tensile strength for zone 2 and zone 3 were higher than the conventional concrete.
It can be concluded that the concrete containing different shape and texture having relatively better tension properties, but lower in compressive strength and work ability properties than conventional concrete.