Maximum Size Of Coarse Aggregate Research Articles

Effects of aggregate sizes on the performance of laterized concrete

Due to the high costs of traditional concrete materials in Nigeria, such as river sand, there is an increasing demand to explore alternative materials like laterite for fine aggregates. Although laterite is abundant in Nigeria, its full potential in the construction industry remains untapped. Previous studies have shown that partially replacing river sand with laterite produces concrete with competitive strength properties. This research aims to validate and extend these findings, evaluating the impact of different aggregate sizes (12 mm, 20 mm, and 40 mm) on the strength of concrete with 10% and 25% laterite replacements for fine aggregate. Results revealed that as the laterite percentage increased, compressive, flexural, and split tensile strengths decreased. While 0% and 10% laterite replacements met the required strength, the mix with 25% laterite fell short. Increasing maximum coarse aggregate size led to higher strengths, with 40 mm sizes exhibiting the highest, and 12 mm the lowest. Compressive strengths ranged from 22.1 to 37.6 N/mm2, flexural strengths from 4.07 to 5.99 N/mm2 and split-tensile strengths from 2.93 to 4.30 N/mm2. This research highlights the need for meticulous mix design adjustments when using laterite, balancing workability with strength objectives. The developed regression models offer a valuable tool for predicting concrete properties based on mix parameters, providing insights for optimizing laterized concrete designs across diverse construction applications and supporting sustainable building practices.

Effects of coarse aggregates size on dynamic characteristics of ultra-high performance concrete: Towards enhanced impact resistance

Coarse aggregates are recently used to address the high production costs and severe autogenous shrinkage of ultra-high performance concrete (UHPC), however, the influence of coarse aggregates size on the dynamic performances of UHPC remains poorly comprehended. Herein, the impact of coarse aggregates on the dynamic performances of UHPC is explored through a multiscale method with the focus on hydration products, micromechanical property, meso-scale fracture and macro-scale dynamic mechanical characteristics. Results show that the increasing maximum coarse aggregates size slightly enhances both the total amount and the elastic modulus of hydration products. The rise of the maximum coarse aggregate size enhances the percentage of fracture across coarse aggregates, thus, improving the impact resistance of UHPC. Regardless of the strain rates, the toughness and dynamic compressive strength enhance with the expanding maximum coarse aggregate size, while the dynamic increase factor and peak strain decrease with the rising coarser aggregates size. The damage degree of UHPC enhances with strain rate but reduces with the increasing maximum aggregate size. A conceptual enhancement mechanism of increasing maximum coarse aggregate size on the impact resistance is proposed. The present results promote the wider engineering application of UHPC containing coarse aggregates.

Influence of aggregate source and size on the shear behavior of high strength reinforced concrete deep beams

This paper aims to examine the influence of coarse aggregate characteristics, including toughness and nominal maximum size of aggregate on the RC deep beams’ shear behavior made with and without shear reinforcement. Nine deep beams were prepared with three coarse aggregate types (i.e., limestone, steel slag, and quartzite) having different toughness properties and two nominal maximum aggregate (10 mm and 20 mm) sizes, which were examined under four-point bending. The experimental findings showed that the deep beams exhibited shear failure caused by diagonal shear cracks initiated between the supports and the loading point. Utilizing bigger coarse aggregate size has led to reducing the number of shear cracks. The deep beam stiffness was not impacted by the change in coarse aggregate toughness, aggregate size, or the use of shear reinforcement. For the beams without shear reinforcement, increasing the nominal maximum coarse aggregate size improved the deep beams normalized shear strength. This improvement depended on the coarse aggregate’s toughness with the toughest aggregate (steel slag) showing the greatest improvement. Moreover, using shear reinforcement has contributed to improving the deep beams’ normalized shear strength. The normalized shear strength increased from 6% to 16% compared to deep beams without shear reinforcement.

Shear friction and fracture based model for reinforced concrete beams with recycled materials

Shear resistance by beams without stirrups presents the transfer of shear and normal principal stresses across the open cracks within reinforced concrete (RC) beams. The complexity of the shear mechanism is further complicated by the distorted structure of RCA, which is composed of hardened adhered surface mortar and virgin aggregate. Compression field theory (CFT) postulates a series of curves for shear-loaded beams to signify the transfer of tensile and compressive stresses in concrete beams across developed shear cracks. Special attention is given to beams with recycled materials, which do not necessarily give the same strength as virgin aggregate. A numerical shear model is developed that accounted for the fracture characteristics, modes I and II of the beam containing RCA along the primary crack path from dowel action, aggregate interlock, and uncracked compression zone of the beam. The model captures the correlation of shear arm ratio, longitudinal reinforcement ratio, maximum coarse aggregate size, and concrete strength. The study model was validated using experimental results from 139 concrete beams containing RCA without stirrups. The strength ratio resulted in mean of 1.32 with a standard deviation of 0.48, a coefficient of variation of 36.8% and R-squared value of 0.65. The statistical evaluations of the model were compared with the other nine (9) theoretical models by authors and codes of practice. The developed model predicted a relatively higher shear strength value due to the inclusion of contribution from dowel action, aggregate interlock and compression zone.

Effect of maximum coarse aggregate size upon shear strengthening of RC beams using NSM-CFRP strips

Reinforced concrete (RC) is widely used because of its many desirable characteristics, such as high strength, fire resistance, and durability. However, structures that are made of concrete may need strengthening or repairing due to concrete deterioration, the harshness of the environment, steel corrosion, errors in design, and damage caused by earthquake load. The use of composite materials has recently become more popular for strengthening and repairing damaged concrete structures. It is also known that properties of the aggregates, such as shape, size, and surface texture, have important influences on the behavior of concrete. In fact, many studies have shown that changes in coarse aggregate will affect the concrete's strength and fracture properties. Towards this end, very little research has been carried out on the effect of maximum aggregate size (MAS) on the shear behavior of reinforced concrete beams. The impact of maximum coarse aggregate size on shear strengthening using the methods proposed in this study was not studied. This research is driven by both environmental and economic aspects where the use of large-size coarse aggregates provides a large volume and less void space compared to small-size aggregates. From an environmental perspective, such an approach will reduce the need for cement in concrete unit volume, hence reducing the pollution. The main purpose of this study is to examine the behavior of reinforced concrete beams under general loading and how this is affected by using different coarse aggregate sizes. This work’s main objective is to investigate the effect of maximum coarse aggregate size on the shear behavior of reinforced concrete beams and study the effectiveness of using the Near Surface Mounted (NSM) – Carbon Fiber Reinforced Polymer (CFRP) strips technique on the shear strengthening of the RC beams. The experimental variables of the study consist of different maximum coarse aggregate sizes (9.5 mm, 12.5 mm, 19 mm, and 25 mm), Carbon Fiber Reinforced Polymer (CFRP) strips spacing (75 mm and 150 mm), and concrete compressive strength (25 MPa and 40 MPa). Fourteen RC beams (150 mm × 200 mm × 1150 mm) were cast using six mixes of concrete to be prepared and tested. The experimental results showed that using maximum coarse aggregate size has a positive effect on ultimate shear strength, maximum deflections, toughness, and stiffness of strengthened RC beams. Using NSM-CFRP strips change the failure mode from pure shear for the control beams to shear-flexural failure for the strengthened beams, which is an ideal enhancement.

Requirements of specimen dimension considering maximum coarse aggregate size for concrete split Hopkinson pressure bar tests

Dynamic increase factors (DIF) of concrete compressive strength have been proposed through experiments on specimens including small aggregates without considering the effect of the coarse aggregate size, which was due to the limitations in the size of specimens and test apparatus. Therefore, this study conducted an experimental investigation of the effect of the maximum coarse aggregate size (Gmax) on the DIF of normal-strength concrete. Split Hopkinson pressure bar (SHPB) tests were performed for mortar and concrete specimens with various sizes of Gmax, and the apparent and pure rate DIFs were obtained. Moreover, the pure rate DIF of each Gmax was verified through numerical analysis of the SHPB tests. The test and analysis results indicated that Gmax affected the dispersion of the apparent DIF and the values of the pure rate DIF. Based on these results, a guideline for the fabrication of specimens considering Gmax for concrete SHPB tests was suggested.

Effect of Aggregate on the Performance of Fly-Ash-Based Geopolymer Concrete

The influence of geopolymer binder characteristics on the performance of geopolymer concrete has been extensively investigated. Yet, the influence of aggregate properties has not been thoroughly studied, and it is usually assumed that their effect is the same as in cement concrete. This study investigates the effect of aggregate on the performance of fly-ash-based geopolymer concrete. A systematic experimental study was undertaken to investigate the effect of aggregate parameters, including volume fractions (AVFs), coarse aggregate to the total aggregate ratio (CAR), maximum coarse aggregate size (MAS), and fineness modulus of fine aggregate (FFM) on the compressive strength, slump, apparent volume of permeable pores (AVPPs), and the air content of geopolymer concrete. Response surface methodology (RSM) using the central composite design approach was utilized to design the experiments and analyze the results statistically. The analysis shows that all of the investigated aggregate parameters have significant first-order effects on the measured properties. No significant interaction between any of the investigated parameters was found. The aggregate may alter the geopolymerization processes, whereby SEM-EDS analysis revealed statistically significant variations in the elemental concentrations of the produced paste as the aggregate parameters changed. Quantitative weights were assigned to the effect of the investigated aggregate parameters on the measured properties. Multi-objective optimization was carried out to obtain the best combinations of the investigated parameters. Additionally, the developed contour graphs may provide an effective tool that can be used as a guide in establishing the first trial mixtures. A wide range of consistencies (10–210 mm slump) and compressive strengths (15–55 MPa) can be obtained by controlling the aggregate grading and proportions.

Effect of concrete mixture on shear behavior of prestressed concrete girders

A total of six shear-critical prestressed concrete (PC) I-girder were tested to investigate the effect of concrete mixture types on the shear behavior of PC girders. The concrete mixtures examined were conventional concrete (CC), high-performance concrete (HPC), and self-consolidating concrete (SCC) with normal (specified fc′=41.4 MPa) and high (specified fc′=68.9 MPa) compressive strengths. Test results showed that the HPC girders exhibited a shear behavior similar to the CC girders, irrespective of the concrete compressive strength. The SCC girder with normal-strength concrete (SCC-N) showed a higher ultimate shear strength ratio (Vult/Vn) and higher ultimate displacement than the corresponding CC girder (CC-N). The SCC-N mixture was designed with a similar coarse aggregate amount but a reduced maximum coarse aggregate size compared with the CC-N mixture. The better performance of SCC-N may be attributed to a better filling ability of the SCC-N mixture than the CC-N mixture. The SCC girder with high-strength concrete showed a lower Vult/Vn than the corresponding CC girder (CC-H). The lower shear strength of the SCC girder may be attributed to the lower coarse aggregate amount (19% lower) than the CC-H girder. A shear test database of PC girders was established to investigate further the effect of coarse aggregate amount on the girder shear strength. Based on the statistical analysis, the Vult/Vn and coarse aggregate amount either showed a positive or insignificant correlation. For those groups of test data that showed positive correlation, the slopes of the linear regression of the test data showed that for a 100 kg/m3 decrease of coarse aggregate amount, the Vult/Vn decreased in average by 18.5%.

Mechanical Behaviour of Self-Compacting Concrete Using Ceramic Waste

The use of Self Compacting Concrete (SCC) which has high workability is the current choice to facilitate casting work so that it can pass through denser reinforcement areas without compaction. The rapidly increasing demand for concrete can cause damage to nature due to the overexploitation of minerals used for concrete such as crushed stone and lime. Construction waste can be an alternative to substitute the use of natural coarse and fine aggregate and an option to reduce gas emissions resulting from processing construction materials such as crushing work and cement production. Moreover, it can increase the efficiency of waste. In this study, ceramic waste is used as a substitute for coarse aggregate, which has the same characteristics as natural aggregate and is usually only dumped in landfill. This study aims to determine the mechanical behavior of SCC using ceramic waste as coarse aggregate substitution with a diameter of 9,52 mm. The mix design uses the Indonesian standard, SNI 7656-2012 with a maximum coarse aggregate size of 9.52 mm and Sika viscocrete 1003 as a superplasticizer. The concrete specimen is 15 cm in diameter and 30 cm in height cylinder of as many as 25 specimens. Design concrete strength is f’c = 25 MPa at 28 days old. The variation of the coarse aggregate substitution of ceramic waste is 0%, 25%, 50%, and 75%, and the 1.5% superplasticizer by the weight of cement. It is obtained that the maximum compressive strength of SCC is a variation of 50% ceramic waste, 25.98 MPa. It showed that the compressive strength did not experience a significant increase, which was only 0.06% increase from the design concrete strength. The stress value also showed a slight increase of 50% ceramic waste variation at 9.42 MPa with a 0.00254 strain value. The modulus of elasticity of concrete at maximum stress is 30,045.89 MPa. It can be concluded that ceramic waste can be used as a substitute for coarse aggregate in SCC. Although it cannot significantly increase the strength of the concrete as well as its stress and modulus of elasticity, ceramic waste substitution for natural aggregate in concrete can minimize the exploitation of minerals in nature and the strength also can exceed the design concrete strength.

Quarry Dust as Partial Replacement for Fine Aggregate in Steel Fiber-reinforced Concrete

The demand for fine aggregate (Natural River sand, NRS) as one of the major constituents in making concrete and masonry blocks increases due to the rapid increase in building construction. This has triggered its scarcity making it an expensive building material. However, quarry dust (QD) has been proven to be abundant in the quarry industry after rock crushing. This experimental study aims at investigating the effect of QD as partial replacement of NRS in steel fiber reinforced concrete. 40%, 50%, and 60% NRS replacement with QD were considered in this study. The fiber content in the mix was 1.5% by the weight of concrete, with a maximum coarse aggregate size of 20mm. The produced concrete cubes targeted 30N/mm2 final strength were examined at curing ages of 7, 14, and 28 days at room temperature. Concrete density and compressive strength were determined for the produced concrete in accordance with British Standards. The laboratory test results of the concrete density and compressive strength ranged from 2533Kg/m3 to 2555Kg/m3, and 38.46N/mm2 to 46.43N/mm2 respectively. The obtained results showed that, maximum compressive strength of 46.43N/mm2 was achieved at 40% replacement. The research outcome indicates the viability of quarry dust as an alternative to natural river sand.

Properties of Concrete Using Bottom Ash N107 Cured in The Tidal Zone

In Indonesia, around 9.89 million tons of Fly Ash and Bottom Ash (FABA)waste is generated annually from burning coal in steam power plants (PLTU). One type of FABA waste categorized as Non-B3 which isBottom Ash with a waste code of N107.Ifthis waste not utilized,itwill only become a waste product. With theIndonesia Government Regulation No. 22 of 2021, this waste utilization process becomes more manageable and has the opportunity to be optimized. One of the recommended alternative uses of Non-B3 FABA is substituting raw materials for infrastructure materials, especially for coastal areas where it is difficult to obtain fine aggregate.In the process of development, coastal areas are often in contact with sea air.Seawater has a high salt content which can undermine the strength and durability of concrete, so this study focuses on discussing the effect of using Bottom Ash as a fine aggregatesubstitute on concrete strengthofthe M24concrete, which is influenced by the sea's tides. By using the ACI 211.1-91 concrete mix design method, experimental concrete samples were made by substituting fine aggregatewith bottom ash N107 with a percentage of 0%,20%and 30% and a maximum coarse aggregate size of 20 mm, the treatment of concrete samples was carried out in freshwaterand in the tidal zone. From the sample of concrete with 20% and 30% bottom ash, it is known that the porosity of the concrete immersed in the tidal zone is higher than that of the concrete immersed in fresh water. For concrete that was given maintenance treatment in the tidal zone, the compressive strength decreased at 56 days.

Developing a support vector regression model via optimization algorithms to appraise the hardness properties of high‐performance concrete

AbstractHigh‐performance concrete (HPC) as a highly sophisticated aggregate in constructional projects has made modeling given mechanical properties a very complex problem. Declaring by many studies, mechanical features of HPC are not only characterized by the maximum size of coarse aggregate and water amount since influencing by the other components. Using fly‐ash and silica fume as the key constituents can simultaneously increase the hardness aspects and the environmental effects. Considering the compressive strength and slump flow of concrete should be investigated before performing any practical practices. Artificial intelligence approaches with precise and low‐cost methods can replace the costly experimental ways. Therefore, the present paper has aimed to link a prediction model with optimization algorithms to accurately appraise the hardness properties of HPC samples rarely found in literature like this way. In this regard, a machine learning approach of Support Vector Regression using two kernels of Gaussian and radial basis function is coupled with matheuristic algorithms to optimize the modeling process of compressive strength and slump flow of HPC samples. The internal settings of SVR would be tuned at optimal rate by optimizers to function efficiently. To investigate the performance of hybrid frameworks developed in this research, several indicators evaluated the results of hybrid models. Therefore, the R2 of the models was calculated averagely at 0.91 with a maximum difference rate of 11% for the testing phase. While the RMSE index assessed the models with higher values of 16.56 mm for slump and 12.86 MPa for compressive strength. Generally, using smart approaches with high‐accuracy performance has been proposed to be used instead of physical procedures increasing the productivity of concrete compressive strength in terms of time, energy, and cost criteria.

FRESH AND HARDENED STATE PROPERTIES OF SCCs PREPARED WITH LIMESTONE-BASED MANUFACTURED AGGREGATES AND POWDER

Because the amount of sand and gravel extracted from natural resources is quickly depleting, the use of manufactured aggregates is becoming increasingly important in terms of sustainability. In this study, crushed limestone and filler material were used as both sand and coarse aggregate and powder material. As a result, all of the concrete components' grains had an angular form and a rough surface. Self-compacting concretes (SCC) were made with a maximum aggregate size of 10 or 16 mm and cement content of 350 kg/m3. The amount of limestone fine was raised in increments of 100 kg/m3 up to 300 kg/m3. The effects of fine material amount and maximum coarse aggregate size on spreading, flow, passing ability through the obstacles, segregation, and rheological properties of SCCs were determined. Although the mixtures' slump flow performances remained in the SF2 and SF3 classes according to EFNARC standards, longer V-funnel times and larger J-ring differences were obtained when compared to slump flow values, particularly for 16 mm aggregate size. The hardened state properties of concretes were examined by measuring the compressive and splitting tensile strengths, modulus of elasticity and Poisson ratio.

FACTORS AFFECTING MIX DESIGN OF CONCRETE

Concrete is a low-maintenance composite material that is primarily composed of cementitious material, water and gravel. It is often used construction material not only in Bangladesh but also across the world. The design of the concrete mix is a critical determinant of the qualities of the concrete. The fundamental ideas and comparative research of certain prominent concrete mix design methods from a qualitative perspective are presented in this work. Two types of concrete mix designs are used which are ACI 211.1-91 (2002) Standard and British Standard (1997) in this paper. Several factors have been determined in this study to choose between the ACI and British Standard. These approaches rely heavily on graphs, tables and bar charts with arbitrary values. The nominal maximum size of coarse aggregate, water to cement ratio (w/c), slump value and the % passing of fine aggregates are used here to change the amount of materials. Differentiating between these strategies allows for a better understanding of the impacts of variables. The ACI and British Standard have been used to compare how the w/c, fine aggregate to cement ratio (FA/C), total aggregate to cement ratio (TA/C) and fine aggregate to total aggregate ratio (FA/TA) are different for various strengths. The following study is expected to pave the path of concrete performance via extensive research on different suggested design factors.

Modelling of Chloride Concentration Profiles in Concrete by the Consideration of Concrete Material Factors under Marine Tidal Environment

The corrosion of reinforcement induced by chloride ions is one of the most significant causes of durability deterioration for reinforced concrete (RC) buildings. The concrete material factors, including the water-to-cement ratio (w/c) of concrete, as well as the content, shape, particle grading, and random distribution of coarse aggregate embedded in mortar, have a marked effect on chloride transport performance within concrete. However, comprehensive consideration for the effects of both w/c and coarse aggregate performances on chloride diffusion characteristics in concrete is scarce, especially regarding the chloride diffusion model of concrete. In this paper, an indoor exposure experiment exploring chloride ions intruding into mortar and concrete specimens with w/c = 0.4, 0.5 and 0.6 was carried out, in order to acquire the chloride diffusion parameters for concrete three-phases composites. Based on the numerical algorithm of random generation and placement of two-dimensional random convex polygon coarse aggregate, mesoscopic numerical models for concrete, considering various coarse aggregate contents as well as grading, were established. Using the numerical simulation method of finite element analysis for chloride transport in cement-based materials, which can replace some of the exposure tests, the influences of w/c, coarse aggregate content and grading on chloride diffusion performance in concrete mesoscopic models were systematically probed. According to the Fick’s second law, a chloride diffusion model by the consideration of w/c, volume fraction of coarse aggregate (VFCA), and maximum size of coarse aggregate (MSCA) was developed to assess the chloride concentration profiles in concrete under arbitrary w/c, coarse aggregate content, and coarse aggregate grading conditions. Certainly, the precision accuracy for this proposed chloride diffusion model was validated. The research results can provide theoretical support for chloride erosion behavior and structural durability assessment of concrete with different mix proportions.

Influence of Distribution Modulus on the Compressive Strength of Ultra-High-Performance Concrete with Coarse Aggregate (UHPC-CA)

The Modified Andreasen and Andersen model (MAA model) is commonly chosen to realize condensed particle packing in ultra-high-performance concretes (UHPCs). In the MAA model, the q (distribution modulus) is a parameter that plays a critical role in the UHPC matrix design. The objective of this study is to figure out the influence of the q for the compressive strength of UHPC-containing coarse aggregate (UHPC-CA). Therefore, a series of investigations were conducted, covering the following aspects: first, the traditional design procedure, based on the MAA model, of UHPC-CA is revised by taking water and steel fibers into account in the particle packing system. The results show that the revised design process of UHPC-CA yielded more excellent products with better workability and compressive strength. Second, different q values which are 0.2, 0.21, 0.22, 0.23, and 0.25 are employed. The results show that when q is 0.25, the maximum compressive strength can be achieved. However, the flowability decreases with the increase of the q value. Third, an empirical calculation of the optimal coarse aggregate content in the light of different q values and maximum size of coarse aggregate are proposed.

Evaluation the Effects of Coarse Aggregates Size on Concrete Properties

Concrete is the most generally used construction material in buildings,pavements, and infrastructures. Concrete is a construction materialcomposed of cement as binder, fine aggregates and coarse aggregatesmixed with water which hardens with time. Concrete is a versatileconstruction material within the housing industry of the planet. Thestandard of the concrete is tormented by various factors and from thosevarious factors which may have an effect on the concrete quality are, thecoarse combination size has its own nice role on the standard of concreteproduction. A laboratorial experiment was conducted to work out the resultscoarse aggregates size on recent and hardened concrete properties. For thisstudy totally different crushed volcanic rock aggregates sizes were collectedfrom almost Jimma city for determination of the results of coarse aggregatesizes in concrete production. Three coarse aggregate nominal sizes of 10mm, 14 mm and 20 mm were used for samples production to envision thescale effects on concrete properties. For this study the procedures that wasfollowed, the types and quantity of materials for concrete creating weresimilar whereas sizes of nominal basaltic coarse aggregate were different.The fresh concrete has a slump value of 67 mm, 72 mm and 83 mm for10mm, 14 mm and 20 mm aggregate sizes respectively. A total of thirty sixconcrete cube samples were ready and tested using compressive strengthtesting machine at totally different ages of the cube 7 days, 14 days, and 28days, to know their strengths. The compressive strength was 23.524 Mpa,22.643 Mpa and 22.41 MPa for aggregate sizes of 10 mm, 14 mm and 20mm respectively. The laboratory results show that 10mm coarse aggregatesize gave the most effective compressive strength and comparativelylowest slump at similar water/cement ratio of 0.6. At 28th day 10mmcoarse aggregate size gave 23.524 Mpa compressive strength which is themaximum compressive strength from the remainder coarse aggregates so,the optimum maximum size of coarse aggregate for this study was 10mm.

Analysis and optimization of mechanical properties of recycled concrete based on aggregate characteristics

Abstract The most significant difference between recycled and natural concretes lies in aggregates. The performance of recycled coarse aggregates directly affects the characteristics of recycled concrete. Therefore, an in-depth study of aggregate characteristics is of great significance for improving the quality of recycled concrete. Based on the coarse aggregate content, maximum aggregate size, and aggregate shape, this study uses experiments, theoretical analysis, and numerical simulation to reveal the impact of aggregate characteristics on the mechanical properties of recycled concrete. In this study, we selected the coarse aggregate content, maximum aggregate size, and the aggregate shape as design variables to establish the regression equations of the peak stress and elastic modulus of recycled concrete using the response surface methodology. The results showed that the peak stress and elastic modulus of recycled concrete reach the best when the coarse aggregate content is 45%, the maximum coarse aggregate size is 16 mm, and the regular round coarse aggregates occupy 75%. Such results provide a theoretical basis for the resource utilization and engineering design of recycled aggregates.

Effects of maximum particle size of coarse aggregates and steel fiber contents on the mechanical properties and impact resistance of recycled aggregate concrete

Fiber reinforced recycled aggregate concrete has become a new type of green concrete material. The maximum particle size of coarse aggregates and steel fiber contents affect the mechanical properties and impact resistance of recycled aggregate concrete. However, such studies are rare in literature. The present paper shortens the gap through experimental study. A total of 144 specimens of 12 kinds of concrete mixtures were tested, which adopted different steel fiber volume admixtures (0%, 0.8%, 1.0%, 1.2%) and recycled coarse aggregates in different maximum particle sizes (9.5, 19, 31.5 mm) replacing 30% natural coarse aggregate. The compressive strength, splitting tensile strength, and impact resistance of the 12 concrete mixtures were tested. The results showed that the compressive strength, splitting tensile strength, and impact resistance of recycled aggregate concrete increased first and then decreased with the increase of the maximum particle size. The recycled aggregate concrete with the maximum particle size of 19 mm had the highest mechanical properties and impact resistance. Besides, with the increase of steel fiber content, the compressive strength, splitting tensile strength, and impact resistance of recycled aggregate concrete showed an increasing trend. Considering a large amount of experimental data and the coupling effect of steel fiber contents and the maximum particle size of coarse aggregates, the Weibull distribution function was introduced to analyze the impact test results and predict the number of resistance to impact under different failure probabilities. The results showed that the number of blows of the recycled aggregate concrete followed a two-parameter Weibull distribution, and the estimated value of the number of resistance to impact for failure increased with the increase of the failure probability.

Experimental Study on Developing High Strength Concrete Mixes as per Indian Standard 10262: 2019

The high strength concrete (HSC) is a special type of concrete, whereas it can resist loads more than that normal strength concrete (NSC) and also, it can increase the speed of construction, early removal of formwork provides early strength and better performance, when compared to NSC. In present study attempts to develop M70 grade HSC mixes using IS 10262:2019. Number of trials for HSC mixes were experimented utilizing marginal materials viz. Ground Granulated Blast Slag (GGBS) and Alccofine as filler. The GGBS content, water content and fine to coarse aggregate ratio were maintained; restricting the maximum size of coarse aggregates restricted to 20 mm. The percentage of alccofines (0% to 12%) and GGBS (20%) replace by weight of cement is kept constants for all the mixes. The water content is also kept constant by varying the water to cement ratio accordingly with replacement of alccofines for cement. The fresh properties (slump test) and hardened properties tests compression strength test, split tensile strength test, flexural strength test) on HSC mixes were carried out as per IS codes. The test result shows that the HSC mixes can be developed by using IS 10262:2019 for given grade of concrete and these developed mixes satisfied both the fresh and hardened properties as per codal provisions. And also results shows that 10% alccofines replacement shows the better workability and strength, when compare to 12% replacement with constant GGBS.