Blended Concrete Mixes Research Articles

An Experimental Study on Properties of Microbial Blended Concrete

Several efforts are being made by researchers to turn concrete into a more sustainable material. Various research are being carried out to substitute cement in concrete, either whole or in part. The current work uses mineral admixtures like metakaolin and GGBS (blended concrete) to partially substitute cement in concrete. Concrete prone to cracking due to structural and Non-structural conditions. All kinds of fissures have the potential to harm concrete by letting water and other substances pass through them, which weakens and distorts the material while also compromising the reinforcing. To repair the concrete cracks, a certain type of treatment and routine upkeep are required, and they will be very costly. So, the current research is to study the impact of Bacteria (microbes) on crack healing as well as on properties of blended concrete. Different mixes of M25-grade concrete were done by using M-sand as fine aggregate to obtain the optimum percentage of GGBS used as supplementary cementitious material (0, 5%, 10%, 15%, 20%, 25%, and 30%), and the same percentage was used in blended concrete, which included metakaolin at different percentages (0, 5%, 10%, 15%, 20%, and 25%).Among different mixes, the proportions of blended concrete with enhanced mechanical properties were considered, and bacteria were induced at a constant percentage in that mix. The results indicated that the microbial blended concrete mix has significantly improved mechanical and durability properties, when compared to conventional and blended concrete mixes.

Accelerated Electromigration Approach to Evaluate Chloride-Induced Corrosion of Steel Rebar Embedded in Concrete

Two distinct binary blended concrete mixes were prepared for the study. The first mix involved a cement replacement of 50% slag, denoted as SL. The second mix incorporated a cement replacement of 20% fly ash, referred to as FA. No chlorides were added during the preparation of these concrete specimens. To accelerate chloride transport, electromigration was employed by placing specimens with varying reservoir lengths (ranging from 2.5 cm to 17.5 cm) on their top surfaces. These reservoirs were subsequently filled with a 10% NaCl solution. In this paper, corrosion propagation was monitored over a period of approximately 650 days using electrochemical measurements such as open circuit potential, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). The evolution of rebar potential, polarization resistance, solution resistance, and corrosion current were analyzed to understand the corrosion behavior. This paper focuses on how the length of the solution reservoirs influences the corrosion-related parameters such as polarization resistance, solution resistance, rebar potential, and corrosion current. During the monitored propagation period, the corrosion current values (last 7 sets of readings) exhibited higher magnitudes for the embedded rebars in specimens made with SL mix in comparison to those made with FA mix. Corrosion current measurements likewise showed an increasing trend as the reservoir lengths increased. None of the specimens had any visible cracks or corroded products that could reach the concrete surface throughout the monitored period. The experimental results provide insights into the corrosion mechanisms and the effectiveness of accelerated corrosion techniques in simulating real-life conditions.

Performance Evaluation of Ternary Blended Concrete Mixes which contains Silica Fume and Bagasse Ash

Cement industries are producing high amounts of carbon dioxide, this problem leads to supplementary cementitious materials utilization. Utilization of agricultural and industrial waste in concrete reduces pollution and disposal problems. This work presents the performance evaluation of the ternary blended concrete mixes in which Silica fume and Sugarcane bagasse ash are used as mineral admixtures. A total of six mixes is used including the Reference mix, which is denoted by M0, M11, M12, M13, M14, and M15 whereas M0 represents the reference mix. M11, M12, M13, M14, and M15 are prepared by partially replacing the cement with SCBA by 5%, 10%, 15%, 20%, and 25% respectively. All the mixes were tested against mechanical and workability properties along with durability Properties and the results are clear that the mix with 15% SCBA and 5% Silica Fume significantly got better results.

Corrosion of carbon steel rebar in binary blended concrete with accelerated chloride transport

Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9 V at first, and subsequently reduced to 3 V after about a week. The electromigration was applied for a short period (few weeks to a couple of months). For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 7 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.

Bond strength of fly ash and silica fume blended concrete mixes

Bond strength of fly ash and silica fume blended concrete mixes

Investigating the performance of ternary cementitious systems incorporating wollastonite powder and lime sludge in concrete

The production of cement results in a significant amount of energy consumption and CO2 emissions, which are major contributors to environmental pollution. Researchers have developed a ternary blended mix concrete to address these concerns by partially substituting cement with a combination of lime sludge (LS) and wollastonite powder (WP). This study investigated the mechanical properties (compressive strength, spilt tensile strength, and flexural strength) of a ternary blended concrete mix with a grade of M30. 180 specimens, including 60 cubes, 60 cylinders, and 60 prisms, were prepared for testing. The blended concrete mix was produced using different percentages of cement replacement by LS (5%, 10%, 15%) and WP (10%, 15%, 20%). The compressive strength for the ternary mix at 10% LS and 15% WP was 44.78% higher than the conventional mix, the flexural strength ternary mix at 10% LS and 15% WP was 25.46% higher than the conventional mix, and spilt tensile strength ternary mix at 10% LS, and 15% WP was 27.30% higher than the conventional mix at 28 days and trend is almost same for 7,56 and 90 days . The results showed that a ternary mix containing 75% cement, 10% LS, and 15% WP exhibited the best mechanical properties.

Prediction of high strength ternary blended concrete containing different silica proportions using machine learning approaches

The most often utilized material in construction is concrete. High plasticity, good economy, safety, and exceptional durability are a few of its characteristics. Concrete is a type of structural material that needs to be strong enough to withstand different loads. The compressive strength of the concrete members is the most crucial mechanical characteristic of concrete because of its brittleness. Furthermore, concrete with ternary blended cementitious materials is a sophisticated composite material. The present study explores the binary and ternary blended concrete mixes with silica fume, ceramic powder, bagasse ash, and alccofine, to determine the compressive and flexural strength. Results of compression strength tests show that mixes, including ultra-fine alccofine, have higher strength. Furthermore, the impact of additional cementitious materials on the surface morphology was examined using scanning electron microscopy on the various mixes. This study investigates using linear regression, KNearest Neighbors (KNN), and Bayesian-optimized extreme gradient boosting to estimate the compressive strength of ternary blended concrete (BO-XGBoost). Using the coefficient of determination (R2), mean absolute error (MAE), and mean square error (MSE), the prediction results are further validated. In comparison, the linear regression and BO-XGBoost models show high accuracy towards the prediction of the outcome as indicated by its high R2 value equal to 0.883 and 0.880, respectively, while the R2 value for KNN is 0.736. Additionally, normalized feature importance was included in determining the input variables that significantly influenced compressive strength. The sensitivity of the model indicates CaO and SiO2 shows significant importance to predict ternary blended concrete compressive strength.

Evaluation of sisal fiber and aluminum waste concrete blend for sustainable construction using adaptive neuro-fuzzy inference system

This research study presents evaluation of aluminum waste-sisal fiber concrete’s mechanical properties using adaptive neuro-fuzzy inference system (ANFIS) to achieve sustainable and eco-efficient engineering works. The deployment of artificial intelligence (AI) tools enables the optimization of building materials combined with admixtures to create durable engineering designs and eliminate the drawbacks encountered in trial-and-error or empirical method. The features of the cement-AW blend's setting time were evaluated in the laboratory and the results revealed that 0–50% of aluminum-waste (AW) inclusion increased both the initial and final setting time from 51–165 min and 585–795 min respectively. The blended concrete mix's flexural strength tests also show that 10% sisal-fiber (SF) substitution results in a maximum flexural strength of 11.6N/mm2, while 50% replacement results in a minimum flexural strength of 4.11N/mm2. Moreover, compressive strength test results show that SF and AW replacements of 0.08% and 0.1%, respectively, resulted in peak outcome of 24.97N/mm2, while replacements of 0.5% and 0.45% resulted in a minimum response of 17.02N/mm2. The ANFIS-model was developed using 91 datasets obtained from the experimental findings on varying replacements of cement and fine-aggregates with AW and SF respectively ranging from 0 to 50%. The ANFIS computation toolbox in MATLAB software was adopted for the model simulation, testing, training and validation of the response function using hybrid method of optimization and grid partition method of FIS at 100 Epochs. The compressive strength behavior is the target response, and the mixture variations of cement-AW and fine aggregates-SF combinations were used as the independent variables. The ANFIS-model performance assessment results obtained using loss function criteria demonstrates MAE of 0.1318, RMSE of 0.412, and coefficient of determination value of 99.57% which indicates a good relationship between the predicted and actual results while multiple linear regression (MLR) model presents a coefficient of determination of 82.46%.

Study on strength and durability characteristics of nano-silica based blended concrete

The present paper highlights on the strength and durability characteristics of blended concrete mixes in different strengths of concrete. A lot of research is being carried out all over the world on various supplementary cementitious materials (SCMs) using various combinations which could be best suitable to achieve strength and durability aspects. Very few emphasized on the usage of Nano-silica as one of the SCMs along with other materials in producing blended concrete mixes. Three SCMs were used in the present study namely fly ash, ground granulated blast furnace slag and Nano-silica as a partial replacement material of cement in various proportions to assess the performance of nano-silica in the development of blended concrete mixes. The great advantages in terms of environmental and economic aspects is the utilization of these three materials (since two of these materials are industrial by-products) point of view. The inclusion of Nano-silica as a SCM up to certain extent can enhance mechanical and durability properties of concrete. Concrete compressive strength increases as the content of Nano-silica increases. Nano-silica has a very high pozzolanic activity. Filling effect of Nano-silica notably influences the refinement of pore structure. The durability properties of blended cement concrete mix were examined by immersing the specimens to HCl and H2SO4 at 5% concentration. Acid Mass Loss Factor (AMLF) and Acid Strength Loss Factor (ASLF) and acid durability factor (ADF) were determined and the results were compared with control mix. Rapid Chloride penetration test (RCPT) on control mix and blended cement concrete were performed to assess the short term chloride ions penetration. From the results, it was shows that the practice of these mineral admixtures is having a beneficiary role on the strength as well as the durability properties. The results indicated that the utilization of these materials as a partial replacement of cement have significantly improved the compressive strength of blended concrete mix in by 36.91%, 27.82% and 19.35% in 29.58 ​MPa, 51.40 ​MPa and 72.33 ​MPa. The results indicated that there is a significant improvement in the mechanical properties, shown better resistance in acid environment and chloride ion penetration.

A study on validation of moment-curvature relationship of lime sludge-based blended cement concrete on numerical modeling (ATENA)

It is evident that the deformation capacity of any RCC structure is always very significant in the flexural design, other than the compressive strength aspect. When a structure is fully-loaded, adequate deformation capacity available in the structure can ensure safety. The present study focused on the flexural behavior of RCC beams consisting of industrial by-products from the paper industry known as lime sludge. The parameters considered in the present study include the strength of control mix concrete (30 MPa, 50 MPa, and 70 MPa), the combination of mineral admixtures (fly ash, silica fume, and lime sludge) as a partial replacement of cement in the preparation of blended concrete mix and type of reinforced section (under-reinforced and over-reinforced beams). Beams of size 1800 mm × 100 mm × 200 mm were cast and tested for flexural strength and the moment-curvature relationships. The improvement in the moment carrying capacity of under and over-reinforced RCC beams was noticed to be 40.12 %, 30.64 %, 22.98 %, 34.80 %, 30.13 %, and 19.44 % in 30 MPa, 50 MPa, and 70 MPa concrete respectively. The curvature of under and over-reinforced concrete RCC beams has improved by 7.64 %, 7.58 %, 7.44 %, 10.30 %, 7.30 %, and 5.15 % in 30 MPa, 50 MPa, and 70 MPa concrete respectively. Validation of the experimental M-ϕ relationship was obtained through the numerical model using FEM-based software ATENA. The experimental results of the moment-curvature relationship are in good agreement with the numerical model.

Strength prediction of sustainable concrete incorporating rice husk ash by using regression technique

In the present scenario, agricultural wastes are used as good replacement material in the construction industry. Rice husk ash (RHa) is used as partial replacement material in the concrete mix and act as pozzolanic materials (PM) for the growth of blended cement. Concrete was prepared by replacing cement with RHa in varying proportions 5%, 10%, 15%, 20%, and 25% by weight of cement) in dry condition. Towards this objective, experiments were carried out in two phases. In the first phase, the strength property of the RHa blended concrete mix was determined separately to get the optimum replacement level and the test includes compressive strength (CS) was performed, and results are presented. Test results reveal that the cement replaced by 10 % RHa enhance the strength of the concrete mix. In the second phase, after performing the experimental tests, mathematical equations were developed using regression analysis to determine the predicted CS. For validation, the correlation between the experimental and predicted CS with time is observed. Results show the 10RHa sample was the best fit model with the highest correlation coefficient of correlation R2 (99.3%). To perform the studies using SEM and EDS along with elemental maps of concrete prepared at optimum conditions to observe the variations in micro structure. Therefore, it can be concluded that RHa in concrete are responsible for enhancing the performance of concrete strength.

Investigation of Abrasion Test and Mechanical Properties of Concrete Using Fly Ash as A Partial Replacement of Cement

Abstract: Concrete is one of the most versatile and widely used material in the construction sector. With the development and advancements of concrete, Civil engineering has reached its technological pinnacle. Despite its global and excessive demands, the consumption of cement is increasing day by day which is to be managed. Also there are many challenges related to its consistent strength performance , Abrasion resistance, Durability etc. so there is a great need to overcome these problems by the application of a pozzolanic admixture known as Fly ash which is responsible for improving various mechanical properties of concrete such as Abrasion Resistance and strength aspects and also reducing the consumption of cement at the same time. In this experimental Work, the Inclusion of Fly Ash and its effect on the various mechanical properties of the concrete i.e. Abrasion resistance, compressive strength, split tensile strength and flexural strength etc is investigated. The present investigation is carried on M35 Grade concrete. Firstly, concrete mixes is prepared by using Ordinary Portland cement( OPC 53) as a reference concrete mix and then blended concrete mixes is prepared by partial replacement of cement using fly ash in range of 10%, 20%, 30%, 40%, 45% by the weight of cement. This experimental study is carried for Determining the differences in the various mechanical properties of blended concrete (Fly ash and cement) and conventional concrete. The optimum percentage of using fly ash with cement in the concrete mixes is determined. The various parameters studies of concrete investigated are Abrasion resistance , workability of freshly prepared concrete mixes, compressive strength at 7 and 28 days, split tensile strength at 28 days. All these tests on concrete mixes is to be performed for both conventional concrete mixes (using only OPC) and also with blended concrete mixes ( OPC and its partial replacements with fly ash).

MECHANICAL PERFORMANCE OF ALKALIACTIVATED CONCRETE INCORPORATING RECYCLED AGGREGATES AND STEEL FIBERS

This study evaluates the mechanical performance of alkali-activated concrete cured at ambient conditions and made with recycled aggregates (RA) and steel fibers. The precursor binder was either ground granulated blast furnace slag or a blend of slag and fly ash (3:1 and 1:1). The alkaline activator solution was a blend of sodium hydroxide and sodium silicate. Coarse aggregates were either natural aggregates (NA) or RA, while fine aggregates comprised desert dune sand. Steel fibers were incorporated, in 2%, by volume, in RA-based concrete mixes. Results showed that replacing NA by 100% RA in plain alkali-activated slag concrete led to decreases of 21, 23, and 51% in compressive, tensile splitting, and flexural strengths, respectively. Meanwhile, alkaliactivated slag-fly ash blended (3:1 and 1:1) mixes experienced respective losses of up to 65, 50, and 57%. The corresponding properties of alkali-activated counterparts made with 100% RA increased by up to 172, 273, and 167% upon the addition of 2% steel fibers, by volume. Yet, the impacts of RA and steel fiber incorporation on the mechanical properties were more pronounced in concrete mixes having higher fly ash replacement. Alkali-activated slag and slag-fly ash blended concrete mixes incorporating 2% steel fibers, by volume, and 100% RA exhibited equivalent compressive strength and superior tensile splitting and flexural strengths to those of NA-based counterparts.

MECHANICAL PERFORMANCE OF ALKALIACTIVATED CONCRETE INCORPORATING RECYCLED AGGREGATES AND STEEL FIBERS

This study evaluates the mechanical performance of alkali-activated concrete cured at ambient conditions and made with recycled aggregates (RA) and steel fibers. The precursor binder was either ground granulated blast furnace slag or a blend of slag and fly ash (3:1 and 1:1). The alkaline activator solution was a blend of sodium hydroxide and sodium silicate. Coarse aggregates were either natural aggregates (NA) or RA, while fine aggregates comprised desert dune sand. Steel fibers were incorporated, in 2%, by volume, in RA-based concrete mixes. Results showed that replacing NA by 100% RA in plain alkali-activated slag concrete led to decreases of 21, 23, and 51% in compressive, tensile splitting, and flexural strengths, respectively. Meanwhile, alkaliactivated slag-fly ash blended (3:1 and 1:1) mixes experienced respective losses of up to 65, 50, and 57%. The corresponding properties of alkali-activated counterparts made with 100% RA increased by up to 172, 273, and 167% upon the addition of 2% steel fibers, by volume. Yet, the impacts of RA and steel fiber incorporation on the mechanical properties were more pronounced in concrete mixes having higher fly ash replacement. Alkali-activated slag and slag-fly ash blended concrete mixes incorporating 2% steel fibers, by volume, and 100% RA exhibited equivalent compressive strength and superior tensile splitting and flexural strengths to those of NA-based counterparts.

Performance Evaluation of Mechanical and Durability Properties of Fly Ash and Silica Fume Based Concrete for Sustainable Building Material

he intensive use of cement in construction is a significant environmental concern. To reduce the use of cement for energy consumption, the use of supplementary cementitious materials (SCMs) like Fly ash (FA) and Silica fume (SF) in concrete is an interesting solution. FA and SF-based construction materials offer a lot of potential as alternatives to ordinary portland cement (OPC) because of their high performance and environmental friendliness. The level of replacement and the necessity for additional cementitious content are critical considerations when choosing the most sustainable material for concrete production. To achieve long-term sustainability, the use of FA and SF in the construction industry is essential. Therefore, the authors attempted to identify the preferred material between FA and SF for sustainability by conducting a performance evaluation on the mechanical and durability properties of two binary mixes, i.e., FA and SF-based concrete mixes. The first binary blended concrete mix is prepared by replacing cement with FA at 20%, 30%, and 40% by weight, and the second mix is prepared with SF at 5%, 7.5%, and 10% by weight. The compressive strength (CS), flexural strength (FS), water sorptivity (WS), and rate of chloride penetration (RCP) of these two binary blended concrete mixes were studied. The results show that the incorporation of SF and FA has a significant impact on workability. The use of SF considerably increased the early and long-term strength of concrete, whereas FA lowered early age strength; nevertheless, it enhanced long-term strength. It was concluded that the SF contributed to better durability properties than FA. FA at 30\% and SF at 10\% exhibited the desired strength and durability than OPC, which can be used as a sustainable building material.

Investigation of sulphate resistance of the nano reinforced blended concrete

In the present study, the control mix (M 30 grade), optimum blended concrete mix containing cement, vetrified tiles powder, silica fume and fly ash and blended concrete mix reinforced with Multi Walled Carbon Nano Tubes were considered and investigated the resistance offered by them against the sulphate attack. The specimens of the respective mixes were immersed in 10% Na2SO4 for a period of 180 days. The optimum blended mix obtained from the previous study contains 60% cement, 7% silica fume, 25% vetrified tiles powder and 8% fly ash. The reinforced blended mixes were developed by incorporating well dispersed Multi Walled Carbon Nano Tubes in the dosage percentages of 0.01%, 0.02%, 0.03%, 0.05% and 0.1% by weight of binder content. The resistance offered by the mixes against the sulfate attack was evaluated in terms of visual investigation, loss in weight, compressive strength and ultrasonic pulse velocity test. Mass loss was observed to vary between 0.3% and 0.7% for the blended specimens and less than 0.2% for the nano engineered blended concrete specimens at 180 days of immersion period when compared to the control mix. The microstructural investigation was carried out using SEM-EDX and XRD to determine the morphology and the formation of the crystalline phases of the matrix after immersion in the solution. From the study carried out it was observed that the reinforced blended mix containing 0.05% of the carbon nano tubes have outperformed all other mixes by exhibiting the highest resistance to the sulfate attack in terms loss of mass, compressive strength and the quality of the concrete. The mix have shown the highest compressive strength value of about 54 MPa at the end of the immersion period which is about 23% higher than the control mix. It can be concluded that the concrete developed not only reduce the carbon foot print on the environment but also contribute towards the high resistance against the sulfate attack.

Evaluation of synergic methods for corrosion protection of reinforced steel

PurposeThis study aims to evaluate the effect of pH on the reinforced concrete steel protection for rebars coated with paint formulations containing talc and free from it. As the presence of talc in paints can offer high pH which cordially affects the protection behavior of the coated rebars. Additionally, this study includes evaluating the durability of concrete mixes in presence of some replacements of ordinary cement such as meta-kaolin (MK) and ground granulated blast furnace slag (GGBFS).Design/methodology/approachTwo paint formulations were prepared containing the same ingredients except that (P1) is free from talc and (P2) contains talc. The anticorrosive behavior of painted steel in the blended concrete mixes containing MK and GGBFS was studied by using different electrochemical techniques in chloride solution. The concrete durability was evaluated by the means of compressive and bond strength beside chloride permeability. Different concrete mixes containing mineral groups or pozzolanic materials were prepared by replacing (10, and 30%) GGBFS and (5, 10 and 15%) MK as binary from cement CEM I with (w/b) 0.45 with superplasticizer ratio (SP) 2% of the binderFindingsIt was found that the presence of talc, in spite of its ability to offer high pH, has affected positively the corrosion behavior of reinforced concrete steel by forming a complex with concrete even if it is present in paint formulation and not free in the medium.Originality/valueThe results revealed that concrete blended with (30% GGBFS and 10% MK) with coated rebars with P2 containing talc showed the highest corrosion protection performance in addition to modified permeability and compression resistance.

Evaluation of Empirical Relation between Compressive and Flexural Strength of Concrete Partially Using Alccofine and Nano-Silica

In this paper, the flexural strength of concrete using alccofine and nano-silica was investigated experimentally and analytically. 15% alccofine and 3% nano-silica by weight of cement was used as a binary and ternary blend in three concrete grades M40, M50, and M60. Compressive strength and flexural strength were obtained experimentally by curing the specimens in water for 28 days. The empirical equation between compressive strength and flexural strength in the form of fr =bfc’n was obtained using regression analysis. The proposed empirical relation was compared with relations given by a code of practices and the relations reported by other researchers for predicting flexural strength using the compressive strength of concrete. The accuracy of the proposed empirical relation was validated using various statistical equations. From the experimental results, it was found that the cubic compressive strength and flexural strength of ternary blended concrete mixes using alccofine and nano-silica was 20 to 29% and 32 to 39 % higher compared to the control mixes. From the values of statistical equations, the proposed relation was found accurate. It showed less error compared to other relations and can be used to determine flexural strength results based on compressive strength data.

Enhancing the performance of Alkali-Activated Slag-Fly ash blended concrete through hybrid steel fiber reinforcement

This paper investigates the mechanical properties of ambient-cured alkali-activated slag-fly ash blended concrete incorporating different hybrid combinations of steel fibers at a volume fraction of 1%. Four types of steel fibers were used with different lengths, degrees of curvature, and tensile strength. The effect of single and hybrid fiber incorporation on the performance of alkali-activated concrete was evaluated, including compressive strength, modulus of elasticity, splitting tensile strength, flexural strength, and shear capacity, toughness, and index (area under the load–deflection curve up to the peak load normalized by the compressive strength). Experimental results showed that hybridization of steel fibers at specific dosages led to superior mechanical properties compared to those without fibers or including a single type of fiber. The mechanical properties were also correlated using analytical regression models and compared to those of the literature and codified equations. A cost-benefit analysis proved that such hybrid mixes were the most cost-effective. Further, newly developed multifunctional performance indices highlighted that the optimum alkali-activated slag-fly ash blended concrete mixes for applications demanding high strength and low cost were those incorporating hybrid steel fibers. The least favorable mixes were those made without fibers or with a single type of fiber. The microstructure analysis revealed an intermix of C-A-S-H and N-A-S-H gels in alkali-activated slag-fly ash concrete.

Binary blended cement pastes and concrete using gravel wash mud (GWM) powders

An alternative supplementary cementitious material (SCM) based on quarry waste sludge, namely gravel wash mud (GWM) powder, is investigated for its performance in blended cement pastes and concretes. Varying mix designs of blended cement pastes and concrete mixtures at Ordinary Portland cement (OPC) substitution degrees from 10 wt% up to 30 wt% by uncalcined and calcined GWM powders were examined at different curing ages using isothermal calorimetry, strength-based examinations, shrinkage test, carbonation test and scanning electron microscopy. The pozzolanic nature of the calcined GWM powder was confirmed, however, minor to no significant physiochemical contributions to the early hydration reactions were observed. The incorporation of calcined GWM powders up to OPC replacement levels of 20 wt% showed an enhancement of the long-term properties of the hardened specimens, namely less drying shrinkage and reduced progression of carbonation compared to the control mixtures. Beneficial strength-enhancing effects were observed for binary blended concrete mixes using calcined GWM powders at OPC replacement levels of 10 wt% and 20 wt% and classified them as viable proportions for alternative SCM-based concretes. The revalorisation of the GWM, a quarry waste product, as a novel and competitive raw material resource for cement production, would provide an environmental-friendly and alternative solution to the expensive and inefficient end-of-life scenario of GWM at the landfills.