Compressive Strength Of Concrete Mixes Research Articles

Mechanical Properties of Concrete Manufactured Using Amorphous Silica and Waste Ceramics: An Experimental Investigation

Researchers are continuously studying the properties and functionality of cement and other aggregates, which are made from a combination of modern materials and different waste. In the current study, a series of experiments were conducted to compare the use of three different types of mixes. In the first mix, amorphous silica was used in place of cement; in the second, Waste Ceramics was used in place of sand; and in the third mix, both materials were combined to create concrete of M20 grade. These materials were used in place of cement and sand in varying amounts, such as 0%, 10%, 15%, 20% and 30%. The properties analyzed were workability by Slump cone and the compressive strengths after 3, 21, and 28 days. The main conclusions is the addition of amorphous silica affects consistency and setting time, as well as increasing compressive strength up to a certain limit. However, it has been observed that workability of concrete increases with the combined use of Amorphous Silica and Waste Ceramic Tiles. Compressive strength: It has been observed Maximum C3 compressive strength is found at 20% replacement of cement with Amorphous Silica after 3, 21 and 28 days of curing. Maximum compressive strength is found at 20% replacement of sand with Waste Ceramics after 3, 21 and 28 days of curing. Maximum XV compressive strength is found at 20% replacement of both cement and sand after 3, 21 and 28 days of curing. Compressive strength of concrete mix was increased slowly when both the chief ingredients were replaced by Amorphous Silica and Waste Ceramic Tiles. Split tensile strength at 3 days, 21 days and 28 days increased up to 20% and then decreases. Flexural strength at 3 days, 21 days and 28 days increased up to 20% and then decreases.

Comparative Analysis of Ensemble Learning Techniques and ANN for Prediction of Compressive Strength of Concrete Mix

Abstract: In this study, non-linear machine learning regressors and an artificial neural network (ANN) were modeled to predict the compressive strength of concrete mixes. A dataset of 1030 mix design data points with a wide range of compressive strength varying from M10 to M80 is taken into account. The data set comprised of 8 input parameters namely- cement, water, fine & coarse aggregate, flyash, slag, superplasticizer, and age. The paper also analyzes effects on the prediction of compressive strength due to waiving of the parameters with lesser importance factors. To improve the performances of models by reducing the variance, biases, and errors, K-fold cross-validation was examined. To examine the performances of the models, metrics such as coefficient of determination (R2) and mean square error (MSE) were employed. Most of the models can predict the compressive strength with good accuracy. Out of the 7-machine learning regressors and ANN models employed, Gradient Boosting Regressor yielded the best prediction accuracy of 0.9561 with the lowest MSE value of 0.0513.

ANN approach to evaluate the effects of supplementary cementitious materials on the compressive strength of recycled aggregate concrete

The growing awareness of environmental issues has triggered significant research into the impacts generated on the environment during concrete production. To improve sustainability in this process, ordinary Portland cement (OPC) and natural aggregates (NA) have been replaced by recycled concrete aggregates (RCAs) and supplementary cementitious materials (SCMs) to reduce the negative issues to the environment. However, the use of SCMs can be challenging due to their complex chemical composition, and RCAs are often of inferior quality compared to NAs, leading to reduced concrete strength. To address these issues, an artificial neural networks (ANN) model has been used for calculating the compressive strength of concrete mixes that oodórate SCMs and RCAs. To train the model, 1181 concrete mixtures from 116 sources were included, considering parameters such as hydraulic reactivity, silica, and alumina modulus. In this research was found that the ANN model is an effective instrument to predict concrete strength even with the use of SCMs and RCAs. The analysis of input variables using the Connection Weight Approach (CWA) concludes that silica fume is the external material that, when mixed with RCA, significantly improves the resistance of concrete, followed by the reactivity modulus of cementitious materials, cement content, silica modulus, fine NA content, and coarse NA dosage. Conversely, excessive ood dosage, high ood/cement ratio, and excessive RCA content (fine and coarse) negatively affect concrete strength.

Modeling the thermal and mechanical properties of early age concrete containing ground granulated blast furnace slag

In this study, a multi-component hydration model of cementitious material was applied to estimate the heat of hydration, adiabatic temperature rise (ATR), and compressive strength of concrete containing ground-granulated blast furnace slag (GGBFS). Different types of GGBFS were hydrated in limewater solution to measure their heat generations. The reference heat of slag in the multi-component hydration model (DuCOM) was revised using the heat measured from each type of GGBFS. Hence, the revised model is sensitive to the chemical compositions of slag. Isothermal and adiabatic heat measurements, as well as compressive strength experiments, were conducted using concrete with four different types of GGBFS. Results show that the proposed model is able to estimate the heat of hydration, adiabatic temperature rise, and compressive strength of concrete mix using different types of GGBFS with various w/cm ratios and air contents. The model predictions versus experimental results show reasonable agreement with the maximum average error percentage of 6.8% and 11% for the heat of hydration and compressive strength, respectively. The proposed method can be a useful technique to obtain the thermal and mechanical properties of GGBFS blended concrete with different cement and GGBFS sources.

Investigating The Combined Effects of Replacing Cement with Sugarcane Bagasse Ash and Coarse Aggregate with Ceramic Tile Waste in Concrete Production

In pursuit of sustainable and innovative construction practices, this study investigates the combined effects of sugarcane bagasse ash (SCBA) and ceramic tile waste (CTW) as subsititue to aggregates on concrete properties, aiming to optimize their usage as eco-friendly alternatives. However, SCBA is a waste product of sugar industry. As a result of increasing recognition and understanding of sustainability and recycling in academia and industry over the past several decades, sustainability and recycling have become increasingly significant. It is also important to note that recycling construction waste and debris is one of the opportunities available for reducing construction waste. To optimize the amount of cement replaced by SCBA, the cement was partially replaced by SCBA and the ceramic waste was replaced at different dosages of 10%, 20%, and 30% by weight of coarse aggregates. Different properties such as workability and compressive strength have been evaluated during 7 and 28 days following replacement by SCBA and CTW. The results further revealed that the workability decreased with the inclusion of SCBA and CTW due to water absorption by the CTW and SCBA particles. However, the compressive strength of concrete mix was relatively higher at 10% replacement of cement by SCBA and 10% replacement of CTW, after which it decreased beyond 10% replacement. The maximum compressive strength was observed as 29.31 MPa with 10% SCBA and 10% CTW at the age of 28 days which is around 9.7% higher than the control mix concrete. It was deduced from the results of this study that 10% SCBA and 10% CTW replacement by the cement and coarse aggregates respectively, could be considered asoptimum replacement.

Quality Assessment of Concrete produced with Marble dust as Partial Replacement of Cement using Ultrasonic Pulse Velocity Test

Cement concrete is one of the most frequently used materials in the construction industry. Constant studies are being carried out to find some alternative material to save natural resources and instead make use of industrial byproducts/waste material which is otherwise polluting the environment. Marble dust which is an industrial waste obtained from sawing, shaping, cutting and polishing of different marbles, is a big environmental hazard. Around 6.8 million tonnes of marble dust is currently being dumped annually in Rajasthan, Gujarat and Madhya Pradesh in India. Although past studies have already investigated the use of this material as a substitute for fine aggregates, since its distribution of particle size is nearer to that of cement, it could be more appropriate for partial replacement of cement in concrete. Cement concrete cubes of size 150 mm were cast as control specimens for two different grades of concrete (M25 Grade and M30 Grade). Effect of marble dust on compressive strength of concrete with varying %age of marble dust as partial replacement of cement is investigated in this study. Marble dust is used as 0, 5, 10, 15 and 20 percent partial substitute of cement by weight in concrete mixes. The compressive strength of concrete mixes is studied at age of 28 days and maximum value of compressive strength is observed at 10% partial replacement of marble dust with cement for both grades of concrete. The quality of concrete so produced is also assessed by using Ultrasonic Pulse Velocity (USPV) method. The ultrasonic pulse velocity is 3850, 4100, 4350 and 3710 m/s for M25 grade concrete and 3870, 4120, 4360 and 3700 m/s for M30 grade concrete for 0%, 5% and 15 % partial replacement of marble dust with cement. As per IS :13311(Part 1):1992 these values of pulse velocities represents good quality of concrete and also justified the use of marble dust in concrete up to 15 percent for both grades of concrete (M25 and M30).

Usage of ready-mixed concrete plant wastewater in concrete with superplasticizer: Effect on physico-mechanical properties

• As the WW content increased, the temperature of the concrete mixtures increased. • The workability of the mixtures is improved at the maximum usage dosage of SP (at 2%). • The air content of fresh concrete is between 2.1% and 2.5%. • The 28-day compressive strength of concrete mixes varies between 37.1 and 41.3 MPa. • The use of washing water on all test days decreased the compressive strength. The rapid growth of population and industrialization increases the demand for concrete day by day. In concrete production, a high amount of waste washing water is released. This waste washing water that is released causes soil and water pollution. This study investigated the fresh and physico-mechanical properties of the concretes prepared with the washing water released in the ready-mixed concrete plants. Wastewater (WW) was used at the rate of 25, 50, 75 and 100 % instead of potable water (PW). In addition, the mixtures used a naphthalene-sulfonate-based superplasticizer (1, 1.5 and 2 %). The effectiveness of SP in concrete produced with WW was also investigated. WW workability was relatively improved in mixtures without SP. However, to increase the workability in mixtures using 100 % WW, the SP dosage should be 2 %. The unit weight of fresh concrete is more than 2300 kg/m 3 . WW ratio and SP dosage did not greatly affect the unit weight of fresh concretes. Increasing the SP dosage decreased the air content of the fresh concrete, while the air content increased as the WW ratio increased. In mixtures with WW, the air content decreased by 20 % when the SP dosage was 2 %. The 28-day compressive strength of concrete varies between 36.9 and 49.00 MPa. It has been determined that C30/37 class concrete can be produced with 100 % WW mixtures. The 28-day compressive strength of the mixtures using 100 % WW decreased by 10 % compared to the reference mixture. As a result, the demand for water or SP increases in concretes using WW. Therefore, approximately 40 MPa compressive strength was obtained in WW concrete produced using SP. By producing concrete using WW, environmental pollution will be greatly reduced.

Metal-Nails Waste and Steel Slag Aggregate as Alternative and Eco-Friendly Radiation Shielding Composites

Metal waste recycling has become a global requirement owing to its environmental benefits and powerful economic activity. Metal nail waste (MNW) is a byproduct of metal nail manufacture. MNW has an equal size, contains a high ratio of iron, and has a high specific gravity comparable to normal aggregate. We present MNW recycling as a partial replacement for fine aggregates and electric arc furnace steel slag (EAFSS) as coarse aggregates to produce sustainable heavyweight concrete (HWC). Our main research aim was to study the radiation shielding and mechanical properties of sustainable HWC by partially replacing MNW with 10, 20, 30, and 40% sand. EAFSS is a coarse aggregate for 60% of the total volume. Fresh and hardened properties of HWC are presented. Furthermore, we analysed the internal structure of HWC mixes using a scanning electron microscope. Our results showed the positive effects of MNW on the unit weight of concrete. The density of HWC mixes ranges between 2650 and 3170 kg/m3. In addition, MNW contributes to increasing the compressive strength of concrete mixes with their use of up to 30%. Therefore, the MNW ratios improved the failure behaviour of HWC mixes. The improved linear attenuation coefficient of HWC mixes was due to using MNW ratios and higher densities than the reference mix.

Mix design of concrete: Advanced particle packing model by developing and combining multiple frameworks

The packing density of a paste matrix and aggregates are considered vital physical parameters that affect the performance of concrete. One way to evaluate the compaction factor of concrete is to use Particle Packing Models (PPM). This approach can be considered one of the effective, sustainable paths that significantly decrease the environmental impacts of concrete by reducing the cement content (as a major cause of greenhouse gas emission) without mitigating its technical properties and enhancing the durability of concrete. There are several PPMs to design well-packed concrete. Nevertheless, most of the models have limitations because they are: used only for conventional concrete or part of the raw materials, outmoded, and require a complicated algorithm. Therefore, this study combined previous PPMs (Abram, Slater and ACI2000-I, Bolomey, Feret and Faury and modified Faury) to propose a novel framework that can overcome the issues that exist in those models. The proposed framework can be used for concrete made with and without supplementary cementitious materials and recycled aggregates and can be simply used and followed up by the concrete industry. The results showed that from 86% of the total mixes with similar w/cement ratios, cement content, and workability classes, the compressive strength of concrete mixes was higher than for those mixes prepared according to the standard mix design. The same conclusion was not shown in the remaining mixes (14%) due to the fact that they used a higher grade of cement strength than the corresponding reference mix. Furthermore, the results show that the proposed framework may significantly reduce the cement content of concrete without jeopardizing/compromising the compressive strength.

Investigating the suitability of sakasaka sand as replacement of natural aggregates in concrete for low volume pavement construction

The demand for access roads to vital services is on the high side in rural areas. This demand face much challenge due to the cost of construction. However, having the opportunity to use non-conventional materials that are naturally available in meeting this demand will ease people living in such environs. It is on this note that an investigation was carried out on an indigenous, naturally available sand popularly known as Sakasaka by Ilesha indigenes to ascertain its suitability for pavement construction. The Sakasaka collected from Ilesha borrow site, Ilesha West Local Government Area of Osun State, was used to produce concrete cubes that were tested after curing for 7, 14, 21, 28, 56, and 112 days respectively to know the strength of the material and compared to theoretical strength. Prior to the cubes production, some investigations such as chemical analysis, Sieve analysis, Specific gravity and so on were carried out on the sand. The study investigates the physical properties, chemical components of Sakasaka as well as the compressive strength properties of the concrete produced at ratio 1:2:4 using Cements A, B, and C 3x brand. The total numbers of cubes cast were 162 with a concrete cube size of 150x150x150mm. Sieve analysis, specific gravity, slump tests were also carried out for different water-cement ratios for the three cement. The concrete cubes were tested at the ages of 7, 14, 21, 28, 56, and 112 days. The effects of cements (A, B, and C) on the all-in-aggregate was investigated with respect to compressive strength at different curing age. From the results obtained, the compressive strengths of cubes were 17.76 N/mm2, 19.92 N/mm2 and 20.5N/mm2 which was in line with the standard compressive strength of concrete mix 1:2:4 at 28days.

Towards Sustainable Concrete Composites through Waste Valorisation of Plastic Food Trays as Low-Cost Fibrous Materials

Recycling of waste plastics is an essential phase towards cleaner production and circular economy. Plastics in different forms, which are non-biodegradable polymers, have become an indispensable ingredient of human life. The rapid growth of the world population has led to increased demand for commodity plastics such as food packaging. Therefore, to avert environment pollution with plastic wastes, sufficient management to recycle this waste is vital. In this study, experimental investigations and statistical analysis were conducted to assess the feasibility of polypropylene type of waste plastic food tray (WPFT) as fibrous materials on the mechanical and impact resistance of concrete composites. The WPFT fibres with a length of 20 mm were used at dosages of 0–1% in two groups of concrete with 100% ordinary Portland cement (OPC) and 30% palm oil fuel ash (POFA) as partial cement replacement. The results revealed that WPFT fibres had an adverse effect on the workability and compressive strength of concrete mixes. Despite a slight reduction in compressive strength of concrete mixtures, tensile and flexural strengths significantly enhanced up to 25% with the addition of WPFT fibres. The impact resistance and energy absorption values of concrete specimens reinforced with 1% WPFT fibres were found to be about 7.5 times higher than those of plain concrete mix. The utilisation of waste plastic food trays in the production of concrete makes it low-cost and aids in decreasing waste discarding harms. The development of new construction materials using WPFT is significant to the environment and construction industry.

Reinforced Concrete Beams Capacity with Various Concrete Compressive Strengths

The use of high-strength concrete (HSC) started about four decades ago in world. Using (HSC) supports the applications in civil engineering such as reduce the size of buildings columns, increase the girders length, increase the buildings stores as well as the economics benefits. The paper aims to investigate the effect of using various compressive strength of concrete mixes on the behavior and load capacity of reinforced concrete beams in terms of cracking, yield, failure loads, deflection and ductility. The experimental program included the cast of six reinforced concrete beams with 1.75 m length and cross section of 200 ϗ 300 mm. The beams specimens were tested under two points loads. Several concrete mixes were tried to obtain the concrete compressive strengths 30.9, 40.3, 51.2, 60.1, 71.6 and 89 MPa that used for every specimen beam. The experimental results showed that the increase of concrete compressive strength developed the load capacity strength and ductility. By increasing the compressive strength ratio with (30%, 67%, 95%, 132%, and 188%) caused increase in cracking load by 25%, 66%, 94%, 116% and 152% respectively, and increased the yield and failure loads by (18%, 31%, 41%, 51%, and 69%), (14%, 32%, 47%, 59% and 77%) respectively. As well as the deflection in yield was decreased by (13%, 22%, 33%, 26% and 13%), while it was increased by 10%, 16%, 23%, 26%, and 39% respectively in failure stage as a result of increased of load failure. Adding to that, ductility is increased by 27%, 50%, 84%, 70% and 61%, respectively with the of increasing of compressive concrete strength in ratios mentioned above.

Effect of ultra-fine fly ash on concrete performance and durability

In the present study ultra-fine fly ash as a novel by-product obtained by a dry and closed separation process was investigated as cement replacement in concrete. The impact of ultra-fine fly ash on material properties was investigated following an upscaling as an approach considering paste, mortar and concrete properties. Two types of cement, Portland cement (CEMI) and slag cement (CEMIII), two types of ultra-fly ashes, one with particle size d90 < 9.3 μm (FA1) and second with d90 < 4.6 μm (FA2) were used. At paste- and mortar- level, cement was replaced at 0%, 15%, 25%, 35% and 50% with FA1 and FA2. At concrete- level, cement was replaced at 0%, 15% and 25% with different ratios of FA1 and FA2. The results at paste- and mortar- level showed that an increased fineness of the fly ash (FA2) contributes to better workability of the mix. For CEMI, the compressive strength of concrete with FA2 at 25% cement replacement was already equal to the reference 0% replacement concrete at the age of 28 days. For CEMIII, the compressive strength of concrete mix with FA1 with 15% and FA2 with 25% cement replacements reached the reference concrete value at the age of 91 days. Regarding the durability, replacing cement with ultra-fine fly ash (FA2) had a positive influence on the resistivity, chloride migration coefficient and alkali-silica reaction (ASR), and a negative influence on the carbonation resistance.

Enhanced Performance of Concrete Composites Comprising Waste Metalised Polypropylene Fibres Exposed to Aggressive Environments

The utilisation of waste plastic and polymeric-based materials remains a significant option for clean production, waste minimisation, preserving the depletion of natural resources and decreasing the emission of greenhouse gases, thereby contributing to a green environment. This study aims to investigate the resistance of concrete composites reinforced with waste metalised plastic (WMP) fibres to sulphate and acid attacks. The main test variables include visual inspection, mass loss, and residual strength, as well as the microstructural analysis of specimens exposed to aggressive environments. Two sets of concrete mixes with 100% ordinary Portland cement (OPC) and those with 20% palm oil fuel ash (POFA) were made and reinforced with WMP fibres at volume fractions of 0–1.25%. The results revealed that the addition of WMP fibres decreased the workability and water-cured compressive strength of concrete mixes. The outcomes of the study suggest that the rate of sulphate and acid attacks, in terms of mass losses, was controlled significantly by adding WMP fibres and POFA. The mutual effect of WMP fibre and POFA was detected in the improvement in the concrete’s resistance to sulphate and acid attacks by the reduction in crack formation, spalling, and strength losses. Microstructural analysis conducted on the test specimens elucidates the potential use of POFA in improving the performance of concrete in aggressive environments.

A review: sustainable compressive strength properties of concrete mix with replacement by marble powder

Purpose: Over the years, various experiments have been performed to investigate the impact of marble powder within the concrete mixture. In the present study, a review has been done to check the persistence of marble dirt as the substitute for concrete constituents. Design/methodology/approach: Furthermore, the impact of marble powder as a replacement of cement and aggregates were reviewed. By reviewing previous studies, the result indicates that the use of waste marble powder in cement and aggregate was adequate to a certain range. Findings: By replacing cement with marble powder in a range between 5% to 10% by weight, it increases the compressive strength of concrete mix by 11.30% to 24.56%, compared to the nominal mix. According to the study, any further increase in the amount of marble powder in place of cement i.e, 12.5% to 20% replacement by weight, results in the reduction of compressive strength of concrete mix by 7.5% to 26.01%. Replacement of aggregates from 5% to 75% with marble powder increases the compressive strength of about 3.22% to 23.91% as compared to the nominal mix. Research limitations/implications: It was also concluded from the current study that, to obtain higher compressive strength, it is advantageous to replace fine aggregates with marble powder than the replacement of cement with the marble powder.

A Comparative Study on Compressive Strength of Concrete Mix Containing Plastic, Glass and Rubber Aggregates

In this study, the behavior of the recycled plastic, glass and rubber tire as partial replacement of coarse aggregate in concrete have been investigated. Polyethylene terephthalate (PET) bottles, one of the waste plastic types, broken glass of bottles and rubber tires are used for these purposes. The reason to choose these to transfer the recycles materials into valuable product and to solve the problem of dumping the tons of plastic waste, broken glass and rickshaw tires. In this study compressive strength of cylinder concrete specimens were carried out at 7 and 28 days curing. Six concrete mixes have been studied, those are—reference specimens with no recycled material (CS0), specimens with 15% plastic (CSP15), specimens with 15% (CSR15) and 30% (CSR30) tire, specimens with 15% (CSG15) and 30% (CSG30) glass. Total 24 cylindrical specimen of 8”x4” were tested for compressive strength. The order of compressive strength was CS0 > CSG30 > CSG15 > CSR15 > CSR30 > CSP15. The Study found that compressive strength of concrete mix decreases with the increase of plastic and rubber content. However, compressive strength of concrete increases with the increase of glass content. Plastic material have low bonding with cement in concrete and perform poorly. On contrary, glass works very well with concrete and compressive strength of concrete reduces with the increase of rubber content.

Fresh properties of recycled aggregate concrete

This investigation intends to characterize the fresh state behaviour of concrete produced with coarse recycled aggregates (CRA). The concrete mixes were produced with different CRA crushing levels (primary crushing or primary and secondary crushing), water to cement (w/c) ratios (0.35, 0.45, 0.55), and paste volumes (±1.25%, ±2.5%). The fresh concrete mixes were tested for slump, flow table, inverted cone, and Vebe. In addition, the workability loss over time was assessed after 0, 30, 60 and 90 min of mixing. The compressive strength of concrete mixes produced after 0 and 90 min of mixing was also related to the workability loss of concrete. The experimental results showed that mixes with CRA and w/c 0.55 tend to have a similar behaviour. This is mainly because in this type of concrete the cement paste plays the dominant role in terms of workability. In mixes with lower w/c (0.35 and 0.45), the shape and texture of CRA became more relevant, leading to less fluidity and consistency. The mixes also showed small scatter of their fresh-state properties for small variations of cement paste volume. For mixes produced with CRA that underwent primary crushing only, the conclusions presented before are valid but the differences are greater.

Optimum usage of GGBS in Ready M ix Concrete Industry.

The construction industry plays a vital role in India’s development and it contributes about 8-10 per cent to GDP on an average. Developing nations like India need to have faster construction with high quality, durability and a pollution-free environment, which can be achieved only with Ready mix concrete (RMC). The usage of GGBS is very high in RMC industry. Compressive strength and workability are the most important and basic properties of concrete for any applications. An experimental investigation is carried out on optimum usage of GGBS in Ready Mix concrete industry. This paper presents the experimental test results of 27 types of concrete mixes made with 10% to 80% replacement of ordinary Portland cement. Slump retention for 180 minute which is a basic requirement for an RMC industry is carried out. Compressive strength testing of all the specimens was carried out at 7, 28, 56, 90 and 180 days. The test results proved that the compressive strength of concrete mix containing GGBS increases but after 50% of the total binder content, the addition of GGBS does not improve the strength of concrete. The reason could be GGBS may act as fine aggregate.

SCOPE OF GRANULATED BLAST FURNACE SLAG AS FINE AGGREGATE IN CONCRETE FOR NORMAL AND FIRE EXPOSURE

Present work experimentally investigates the scope of utilizing granular blast furnace slag (GBFS) in concrete exposed to high temperature. Six series of concrete mixes of Grade M20 including control mix were prepared by replacing natural sand with GBFS in 10, 30, 50, 70 and 100% by weight. Sustainability of GBFS concrete for normal weather condition was ensured by preliminary investigation on mechanical strength for various GBFS concrete mixes at various ages. Later, fire durability of the concrete was evaluated by residual compressive strength, weight loss and surface observation of heat cured specimen through necked eye. Cube compressive strength improves by 2.15-6.31% while cylindrical compressive strength of concrete mix with 30% GBFS marginally improves at all ages. Split strength increases up to 2.9-8.07% up to 50% GBFS replacement while flexure strength increases by 0.81-7.0% at 30% with respect to all the age of curing at room temperature. Residual compressive strengths were 57.3, 55.89 and 54.46 % for 30, 50 and 70% GBFS concrete mixes at 600°C. Surface cracks in specimen were observed after 500°C which continued to grow with the increase in temperature. Furthermore, test results indicate the improvement in the properties of concrete with the incorporation of GBFS even though it exposes to high temperature.

Indirect evaluation of the compressive strength of recycled aggregate concrete with high fly ash ratios

In this study, the compressive strengths of concrete mixes made with high incorporation of fly ash (FA) and recycled concrete aggregates (RCA), individually and jointly, with and without superplasticisers (SP), were evaluated by non-destructive ultrasonic pulse velocity (UPV) test. Three mix families (0, 30 and 60% FA) were produced and, for each of these three families, three incorporation levels (0, 30 and 60%) of fine RCA were used with 0% and 100% of coarse RCA, with and without SP. In this study, the effects of each of these materials on the UPV of concrete mixes were determined. Different equations are proposed to predict the compressive strength of concrete mixes by means of the non-destructive UPV, according to their mix composition. Moreover, in cases where the FA content is known, as the oven-dried density of concrete can be easily determined, a simplified expression is proposed to estimate the compressive strength of concrete mixes according to their density and FA ratio (in terms of cement mass), regardless of the type and content of aggregates and content of the admixture, within the limits tested in this research.