For the purpose of mixture proportioning, it is important to know the space occupied by the aggregate particles, including the pores within the particles. The BSG of an aggregate is not directly related to its performance in concrete, although, the specification of BSG is often done to meet minimum density requirements.
The purpose of this research was to investigate the influence of natural coarse aggregate coatings on physical properties of concrete and to establish how each of the three common monitoring tests (ASTM C117, Caltrans Test No. 227, and AASHTO TP57) predict the influence of these coatings on the quality of the resulting concrete.
Two combined aggregate gradation bands were used to develop the proposed mix design since those were proved to perform well in the mix and the resulting concrete exhibited insignificant variation in fresh and hardened properties. It was found that RHA incorporation within cement significantly reduced the permeability of resulting concrete.
From the obtained results, it is observed that omission of smaller size aggregates has least effect (3%) on compressive strength. On the other hand, if larger sizes are omitted, then the residual strength of the concrete is about 67%. ...
Combination of fine and coarse aggregates to achieve the lowest void volume. The amount of cement paste used in concrete depends on aggregate particle packing, where the denser combination among particles with different particle sizes results in a minimum volume of voids (Vv).
Effect of coarse aggregate sizes in concrete : As the sizes of coarse aggregate increases then the compressive strength will also increase with constant water to cement ratio(w:c -0.5 and Mix proportion 1:2:4) The workability of concrete get improved after increasing larger sizes of aggregates in concrete.
The results show that, workability of concrete decreased as fines content increases. At the same level of fines content, workability increases when the W/C increased. The study again revealed that up to 4% fines content, compressive strength increased as the fines content increases.
They concluded that, in high-strength concretes, higher strength coarse aggregates typically yield higher compressive strengths, while in normal-strength concretes, coarse aggregate strength has little effect on compressive strength.
The workability of fresh concrete increases with poor gradation of the coarse aggregate. The workability of fresh concrete is higher for gap graded coarse aggregate concrete than for well graded coarse aggregate concrete. For the gap aggregates, the bigger the particle sizes removed, the higher the workability.
The bigger the size of the aggregates the lesser is the surface area hence less amount of water is required for wetting the surface. Hence less paste is required for lubricating the concrete surface to reduce internal friction, thus we can say that the bigger size of aggregates will give higher workability.
Mix design of concrete cannot be carried out without specific gravity of fine aggregate, and higher specific gravity produced stronger concrete. Finally, the presence of silt in sand would increase water demand in concrete mixture and may reduce concrete strength.
Maximum Aggregate Size As the maximum size of coarse aggregate reduces, surface area of coarse aggregate increases. Higher the surface area, greater is the water demand to coat the particles and generate workability.
The strength of concrete also increases with the increase in size of coarse aggregate for a cement content of 150 kg/m3. However, for concrete with cement content more than 150 kg/m3, strength increases with the increase in size of coarse aggregate upto 25 mm and decreases as the aggregate size increases beyond 25 mm.
Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch sieve. Coarse aggregates are any particles greater than 0.19 inch, but generally range between 3/8 and 1.5 inches in diameter.
Factors which affect workability of concrete are:Cement content of concrete.Water content of concrete.Mix proportions of concrete.Size of aggregates.Shape of aggregates.Grading of aggregates.Surface texture of aggregates.Use of admixtures in concrete.More items...•
Aggregate is commonly considered inert filler, which accounts for 60 to 80 percent of the volume and 70 to 85 percent of the weight of concrete.
Aggregate are the important constituent in concrete. They give body to concrete, reduce shrinkage and affect economy. Earlier, aggregate were considered chemically inert but now it has been recognized that some of the aggregate are chemically active and also certain aggregates exhibit chemical bond at the interface of aggregate and paste.
aggregate. Or as the ap proximation, concrete consists of two
This is based on the measurements of the intercepts of mortar layers among coarse aggregate particles in the finished concrete. Various kinds of concrete are analyzed.
Concrete can absorb moisture because of its porous nature. When ambient relative humidity is high, concrete will absorb moisture from the air. When relative humidity is low, water will evaporate from the concrete in to the ambient environment. This absorption of moisture by concrete causes dampness in roof slabs and when concrete is more porous dampness will be higher. Porosity in concrete especially in roof slabs is caused by following several factors; Poor mix proportion, Poor compaction and laying, Curing regime, Poor construction practices.And dampness in roof slab which is primarily absorption of moisture by concrete is caused by following factors; Porosity of concrete, Relative Humidity, Surface area of element, Exposure period of wetting and drying.
often vibrated to achieve good compaction in concrete.
The coefficient of thermal expansion (CTE) was determined for a typical concrete-paving mixture made with six different types of coarse aggregates belonging to the basic class of glacial gravel, quartzite, granite, diabase, basalt, and dolomite. The CTE, compressive strength, and splitting tensile strength of fifteen different concrete mixtures were determined at the age of 28 days. Two parameters, CTE and splitting tensile strength, are the basic input in AASHTO's new mechanistic-empirical pavement design method. The study revealed a no-ticeable variation in the values of the CTE of concrete with different types of aggregates. Concrete with quartzite aggregate had the highest value of the CTE followed by dolomite, glacial gravel, granite, and diabase or basalt. The estimated value of the splitting tensile strength of concrete, considering its compressive strength and using AASHTO's Mechanistic-Empirical Pavement Design Guide for Level 2 design of concrete pavements was discovered to be significantly lower (17–31%) than its actual experimentally determined value.
The effect of shape, texture and grading of aggregates on fresh concrete was evaluated experimentally, quantified by means a proportioning
supplementary cementing materials can be used to improve the workability of concrete with high microfines without negatively affecting hardened
rounded, and smooth particles require less paste for a given slump than blends with flat, elongated, angular, and rough particles. At the same time,
concrete can be made with MFA with high-microfines content.
The report does not constitute a standard, specification, or regulation.
The elongation index of an aggregate is defined as the percentage by weight of particles whose greatest dimension (length) is 1.8 times their mean dimension. This test is applicable to aggregates larger than 6.3 mm. Elongation gauge (see Fig-5) is used for this test. This test is also specified in ( IS: 2386 Part-I ). However there are no recognized limits for the elongation index.
Tests on Aggregate. Aggregate plays an important role in pavement construction. Aggregates influence, to a great extent, the load transfer capability of pavements. Hence it is essential that they should be thoroughly tested before using for construction. Not only that aggregates should be strong and durable, they should also possess proper shape ...
The test consists of subjecting the specimen of aggregate in standard mould to a compression test under standard load conditions (See Fig-1). Dry aggregates passing through 12.5 mm sieves and retained 10 mm sieves are filled in a cylindrical measure of 11.5 mm diameter and 18 cm height in three layers. Each layer is tamped 25 times with at standard tamping rod. The test sample is weighed and placed in the test cylinder in three layers each layer being tamped again. The specimen is subjected to a compressive load of 40 tonnes gradually applied at the rate of 4 tonnes per minute. Then crushed aggregates are then sieved through 2.36 mm sieve and weight of passing material ( W2) is expressed as percentage of the weight of the total sample ( W1) which is the aggregate crushing value.
Abrasion test is carried out to test the hardness property of aggregates and to decide whether they are suitable for different pavement construction works. Los Angeles abrasion test is a preferred one for carrying out the hardness property and has been standardized in India ( IS: 2386 part-IV ).
After specified revolutions, the material is sieved through 1.7 mm sieve and passed fraction is expressed as percentage total weight of the sample. This value is called Los Angeles abrasion value.
Aggregates to be used for wearing course, the impact value shouldn’t exceed 30 percent. For bituminous macadam the maximum permissible value is 35 percent. For Water bound macadam base courses the maximum permissible value defined by IRC is 40 percent.
In order to decide the suitability of the aggregate for use in pavement construction, following tests are carried out: Crushing test. Abrasion test. Impact test. Soundness test. Shape test.
Grading of aggregate is the particle size distribution, which is determined by sieve analysis. The particle size distribution of a mass should be such that, voids between the coarse aggregate should be filled by fine aggregates. The grading of the aggregate affects the workability of concrete. When grading of aggregate is done by sieve analysis.
The grading pattern of a sample is assessed by a sieving air-dried sample of specified weight through all the sieves. The sieves are mounted one over another in order of reducing opening size. Sieving is performed manually or mechanically to give motion in all possible directions till almost no particle is passing through. The sample should be free from lumps of fine particles to prevent clogging of the finer sieves. When the minimum weight of the sample to be taken for sieving depending on the maximum size present in substantial proportions in the aggregate standardized. When IS CODE2386. Minimum weight of the sample.
It is defined as the sum of the cumulative percentages retained on the sieves of the standard series ranging from 80mm to 150microns and dividing the sum by 100. When all particles in a sample are coarser then say 600µm, the cumulative percentage retained on 300µm, 150µm should be entered as 100.
The maximum weight retained on a sieve after sieving is restricted to avoid overloading and retaining finer fraction in the portion retained. When the material is split into parts and each position is sieved separately.
The same fineness modulus can represent a number of different size distributions and grading curves. Therefore, fineness modulus cannot be used as a description of the grading of aggregate. When the use of the fineness modulus in the assessment of variations from the same source or parabolic behavior of a concrete mix is of great help.
Strength and stiffness are the key parameters characterising the bond performance of fibres in concrete. However, a straightforward procedure for estimating the bond parameters of a synthetic macro-fibre does not exist. This study employs pull-out tests to investigate the bond behaviour of synthetic macro-fibres. Two types of macro-fibres available in the market were investigated. A gripping system was developed to protect the fibres from local damage. The experimental campaign consisted of two stages. At the first stage, 32 concrete specimens were manufactured for performing 96 pull-out tests (three fibre samples were embedded in each cube perpendicular to the top surface and two sides). Two types of macro-fibres with either 10 mm or 20 mm embedment length were tested. The obtained load-displacement diagrams from pull-out tests demonstrate that the bond performance (characterised by the strength and deformation modulus) of the “top” fibres is almost 20% weaker than fibres positioned to the side surfaces. At the second stage, one type of macro-fibre was chosen for further experimentation of the feasibility of improving the bond performance through the use of colloidal silica or steel micro-fibres. This investigation stage employed an additional 36 concrete specimens. The use of steel micro-fibres was found to be an efficient alternative. The success of this solution requires a suitable proportioning of the concrete.
The behavior of Fiber Reinforced Concrete (FRC) depends on the characteristics of both the concrete matrix and fibers. Previous studies have concluded that the number of hooked ends increases the contribution of steel fibers to the tensile performance of concrete. ACI 318 code, MC10 fib code and RILEM TC 162-TDF standard permit the use of Steel Fiber Reinforced Concrete (SFRC) e.g., the minimum shear reinforcement made of deformed steel bars in flexure-controlled elements. Other investigations have demonstrated the suitable performance of SFRC in shear-controlled members and for seismic rehabilitation applications. It has become apparent that the adequate use of SFRC depends on the knowledge and prediction capabilities of its tensile performance. The results of three-point bending tests (3PBT) on SFRC beams using the test procedure established by the European standard EN-14651 are presented and discussed herein. Tests were executed with 20 standardized beams made of concrete with a nominal compressive strength of 24 MPa and hooked end steel fibers with an aspect ratio of 65 were applied. Variables were the fiber dosage (0, 20, 40, 60 kg/m 3) and the number of fiber hooked ends (1, 1.5 and 2). A numerical model aimed at estimating the residual flexural tensile strength of the SFRC is developed. The proposed model was calibrated using a database of 256 tests, 20 from this study and the remaining 236 from 15 other studies.
Steel fiber reinforced concrete (SFRC) is a special type of concrete of which the use of this concrete type is growing up. With the wide using of SFRC, some requirements have emerged. One of these requirements is a practical mix design of SFRC. In this study, it is aimed to produce an effective mix design nomogram, including both fresh and hardened properties of SFRC, simultaneously. With this aim, the relationships between mixture proportions, fresh and hardened properties of SFRC were revealed with the convenient graphics, and these were brought together to create a nomogram. As different from previous studies, two most important superior mechanical properties of SFRC such as flexural strength and modulus of toughness were included in the developed mix design nomogram. As a conclusion, two nomograms which help to accurately and practically estimate mix design of SFRC with aimed properties were revealed. Using these nomograms, at academic milieu and institutions for SFRC, it can be possible to minimize loss of material and time during trial-and-error sample production. Thus, the production process of SFRC can be achieved more practically and economically.
The morphological characteristics of coarse aggregates, namely shape profile, angularity and surface texture , have a significant effect on the mechanical properties of asphalt mixtures. The identification methods and evaluation indexes of the morphological characteristics are crucial for the coarse aggregates. First, the visual identification technologies, including charged coupled device (CCD)image processing, X-ray tomography imaging and laser scanning technology, are summarized in term of the characteristics, research status and existing problems. Based on the deficiencies of visual identification technologies, it is proposed to improve the three-dimensional reconstruction of aggregate particles by increasing the number of two-dimensional projection directions or scanning sections. Moreover, the evaluation indexes of coarse aggregate morphology were summarized from the three aspects, namely shape profile, angularity and surface texture. It is found that evaluation of the indexes based on two-dimensional profile images or unrelated to pavement performance could not adequately evaluate the morphological characteristics of coarse aggregates. Therefore, the evaluation methods and indexes of coarse aggregate morphological characteristics have been recommended based on the performance of asphalt mixtures in this paper, which is helpful to establish a complete set of an evaluation system for coarse aggregate morphology.
Macroperformance, i.e., skid resistance, high-temperature, and compaction performance, are related to the functional performance, safety, and durability of asphalt pavement. Currently, the research on such influencing factors focuses on the properties of asphalt, gradation composition, pavement structure, and so forth, whereas the geometrical characteristics of coarse aggregate, especially its angularity, has not gained due attention from researchers. This paper investigated the effects of coarse-aggregate angularity on the skid resistance, hightemperature performance, and compaction performance of asphalt mixtures. Three-dimensional angularity (3DA) computed by X-ray computed tomography (XCT) was employed to characterize coarse-aggregate angularity. Texture depth (TD) and British pendulum number (BPN) were evaluated through the sand patch test and the British pendulum test (BPT), respectively. The dynamic stability and rutting depth of mixtures with different coarse-aggregate angularities were examined with the wheel tracking test. The variation in height of the specimen with different angularity asphalt mixtures during the compaction process was tested through the Superpave gyratory compactor (SGC). The dynamic modulus (jEj) of the asphalt mixtures was analyzed with the asphalt mixture performance tester (AMPT) and the generation of master curves. The results showed that three-dimensional (3D) angularity is able to characterize the angularity of the coarse aggregate. A lower coarse-aggregate angularity leads to a smaller skid resistance of the asphalt mixture. The angularity greatly influences the high-temperature and compaction performance of asphalt mixtures. Higher angularity leads to better high-temperature stability but causes difficulty in compaction. The angularity has a significant influence on the jEj values of SMA-16 asphalt mixture. The results revealed that the decrease in coarse-aggregate angularity translated into a decrease in jEj values on average. This study provides support for further research into and application of macroscopic properties of asphalt mixtures.
The present study investigated the application potential of crushed gravel (CG) aggregates in asphalt mixes. Three different types of aggregates; i.e., gravel (G), crushed gravel (CG), and crushed stone (CS); were used for shape characterization and mix performance evaluations. The CG aggregates were produced by crushing G aggregates using a single-stage jaw crusher. The aggregates of six different sizes; i.e., P19-R12.5 (passing through 19 mm and retaining on 12.5 mm), P12.5-R9.5, P9.5-R4.75, P4.75-R2.36, P2.36-R1.18, and P1.18-R0.600; were considered in this study. The aggregate was subjected to shape characterization using a digital image-based aggregate image measurement system (AIMS). The cumulative shape index (CSI) for each aggregate shape parameter was determined for three control (i.e., 100% G, 100% CG, and 100% CS) and three mix blends (i.e., 25% CG + 75% CS, 50% CG + 50% CS, and 75% CG + 25% CS). The performance of the asphalt mixes under shear, compression, and moisture damage was evaluated using an aggregate slip test (AST), stability (S), and moisture damage potential tests, respectively. Additionally, the correlations between mix performance and CSIs were drawn. The results showed that the crushing of G aggregates significantly improves the angularity, texture, and form2D, but decreases the sphericity. The CG aggregate angularity increases with the decrease in aggregate size. The gradation with 100% G had the least cumulative angularity index (CAI) and cumulative texture index (CTI) followed by the 100% CG and the 100% CS gradations. However, in the cases of cumulative sphericity index (CSpI) and cumulative form2D index (CF2DI), varying trends were observed. The performance tests revealed that all but the 100% G mix combinations satisfied the stability and moisture resistance criteria of asphalt mixes. Also, mixes with 100% CG aggregates offered a relatively higher rutting resistance than the 100% G aggregates. The CAI, CTI, and CSpI exhibited positive correlation with stability and rutting resistance, whereas the CF2DI showed negative correlation. Further, the AST test more effectively captured the effects of aggregate shape than stability. The study concluded that even 100% CG aggregates can be used in asphalt mixes without any detrimental effects on performance.
The quality of rock aggregates for a given usage is determined by many different test methods, one of the most important of which is the Los Angeles abrasion (LAA) test as it is used to evaluate the resistance to abrasion and wear of aggregates for such applications as railroad ballast, base course material, and asphalt and concrete aggregates. In this study, the relationship between rock texture and LAA loss was investigated for 26 sources of carbonate aggregates found in Iran which constitute the most commonly quarried crushed rock. Regression analyses were used to determine whether rock texture was a useful predictor of LAA loss. The texture of rock aggregate was quantified by texture coefficient (TC), which can be used to put a value on rock texture with studies carried out on the rock thin section using image analysis. In addition, the effects of textural parameters including area weighting of grains or packing density, grain shape, grain elongation, circularity, and orientation of mineral grains, and also TC on the LAA loss were evaluated. Although the results show that weak relationships exist between textural parameters and LAA loss, a strong relationship exists between TC and LAA loss. The results indicate that many textural parameters, together with TC, can be interpreted as rock texture which influences the LAA loss. Also, the results indicate a strong negative correlation between LAA loss and TC, and can be used to predict LAA loss in practical applications.