Effect Of Mix Design Parameters Research Articles

Effect of mix design parameters on the behavior of compression cast concrete

Compression casting is a novel method for producing high-performance concrete. However, the optimal mix design parameters for normal concrete (NC) may not be suitable for compression cast concrete (CCC) due to the high compression pressure involved during casting. This study addresses the lack of research on CCC mix design and examines the influence of different parameters, including aggregate gradations, maximum particle size, sand ratios, and water-to-cement (w/c) ratios, on the performance of NC and CCC. Fourteen groups of concrete samples were prepared with varying aggregate grading, particle sizes, sand content, and w/c ratios. The density, compressive strength, elastic modulus, peak strain, and stress-strain behavior were analyzed. CCC specimens exhibited superior stress-strain relationships compared to NC specimens. CCC can be produced with different aggregate gradings and particle sizes. Notably, CCC specimens with a maximum aggregate size of 25 mm and no particles between sizes 5 mm and 9.5 mm (grading - 4) demonstrated the highest compressive strength and elastic modulus. CCC specimens with a sand ratio of 38% outperformed those with ratios of 28% and 48%. Increasing the w/c ratio showed similar stress-strain behavior for both NC and CCC specimens. This study proposes relationships between the properties of NC and CCC based on the findings. The results provide valuable theoretical and experimental insights for engineering applications involving CCC, considering different aggregate grading, particle size, sand ratio, and w/c ratio combinations.

Multi-Response Optimization of Semi-Lightweight Concrete Incorporating Expanded Polystyrene Beads

The utilization of expanded polystyrene (EPS) beads in semi-lightweight concrete (SLC) intended for repair and building applications has gained great attention in recent years. This study examines the effect of mix design parameters including binder content, water-to-binder ratio (w/b), EPS content, and silica fume (SF) additions on the mechanical properties and durability of SLC mixtures. The experimental program was carried out following the Taguchi approach for four parameters, each having three levels, to produce an L9 orthogonal array. The performance criteria under investigation were the superplasticizer demand, density, compressive strength, splitting tensile strength, ultrasonic pulse velocity, water absorption, sorptivity, and abrasion resistance. Test results showed that the w/b and EPS content were the most contributing parameters that altered the SLCs performance. The multi-response optimization method (TOPSIS) revealed that superior performance could be achieved using a binder content of 375 kg/m3, a w/b of 0.45, an EPS content of 3 kg/m3, and a SF replacement rate of 8%. The mix design parameters were utilized to create multivariate regression models to predict the SLCs mechanical and durability properties. Such data can be of particular benefit to engineers seeking the use of lightweight materials for sustainable construction with optimized durability and a reduced cement carbon footprint.

Mitigating environmental impact by development of ambient-cured EAF slag and fly ash blended geopolymer via mix design optimization.

This article discusses the utilization of industrial by-products, namely, electric arc furnace slag (EAFS) and fly ash to produce cementless geopolymer binder. Taguchi-grey optimization is used for experimental design and for investigating the effects of mix design parameters. Fly ash, in the levels of 0-75% (by mass), partly replaced EAFS in the binary-blended composite system. Experiments were performed on the microstructural development, mechanical properties, and durability of ambient-cured EAFS-fly ash geopolymer paste (EFGP). The optimal mix with 75-25% composition of EAFS and fly ash produced ~ 39MPa compressive strength accrediting to the co-existence of C-A-S-H and N-A-S-H gels. The initial and final setting times were 127min and 581min, respectively, owing to adequate alkali and amorphous contents in the matrix, and the flowability was 108% due to sufficient activator content and the spherical shape of fly ash particles. SEM, XRD, and FTIR results corroborated the mechanical test results.

Optimization of Pervious Geopolymer Concrete Using TOPSIS-Based Taguchi Method

This paper evaluates the effect of mix design parameters on the mechanical, hydraulic, and durability properties of pervious geopolymer concrete (PGC) made with a 3:1 blend of granulated blast furnace slag (GBFS) and fly ash (FA). A total of nine PGC mixtures were designed using the Taguchi method, considering four factors, each at three levels, namely, the binder content, dune sand addition, alkaline-activator solution-to-binder ratio (AAS/B), and sodium hydroxide (SH) molarity. The quality criteria were the compressive strength, permeability, and abrasion resistance. The Taguchi and TOPSIS methods were adopted to determine the signal-to-noise (S/N) ratios and to optimize the mixture proportions for superior performance. The optimum mix for the scenarios with a compressive strength and abrasion resistance at the highest weights was composed of a binder content of 500 kg/m3, dune sand addition of 20%, AAS/B of 0.60, and SH molarity of 12 M. Meanwhile, the optimum mix for the permeability-dominant scenario included a 400 kg/m3 of binder content, 0% of dune sand addition, 0.60 of AAS/B, and 12 M of SH molarity. For a balanced performance scenario (i.e., equal weights for the responses), the optimum mix was similar to the permeability scenario with the exception of a 10% dune sand addition. An ANOVA showed that the binder content and dune sand addition had the highest contribution toward all the quality criteria. Multivariable regression models were established to predict the performance of the PGC using the mix design factors. Experimental research findings serve as a guide for optimizing the production of PGC with a superior performance while conducting minimal experiments.

Development and Optimization of Geopolymers Made with Desert Dune Sand and Blast Furnace Slag

This study assesses the effect of mix design parameters on the fresh and hardened properties, cost, and carbon footprint of geopolymer mortar made with desert dune fines (DDF) and blast furnace slag (BFS). Taguchi method was employed in designing the experiments. Four factors were considered, each having three levels, leading to a total of nine geopolymer mortar mixes. The factors comprised the DDF replacement percentage, alkali-activator solution to binder ratio (AAS/B), sodium silicate-to-sodium hydroxide ratio (SS/SH), and sodium hydroxide (SH) molarity. Ten performance criteria were evaluated, including the flowability, final setting time, hardened density, 1, 7, and 28-day compressive strengths, water absorption, sorptivity, cost, and carbon footprint. ANOVA was carried out to estimate the contribution of each factor towards the response criteria. Further, TOPSIS analysis was utilized to optimize the mixture proportions of DDF-BFS blended geopolymer mortar. Experimental results showed that up to 25% DDF replacement enhanced the density, strength, and durability of the geopolymers with minor impact on the flowability and setting time. Higher replacement percentages had a detrimental impact on the performance but could still be utilized in specific mortar construction applications. The other factors had more limited contributions to the performance, evidenced by the ANOVA. TOPSIS method revealed the optimum mix to be made with DDF replacement of 25%, AAS/B of 0.5, SS/SH of 1.5, and SH molarity of 10 M. Different multivariable regression models were also developed to predict the fresh and hardened properties of the DDF-BFS geopolymer mortars using the mix design parameters.

Influence of concrete mix proportions on lifetime flexural load-bearing capacity of RC beams under chloride corrosion of rebars

In this research, the effects of mix design parameters on chloride ion diffusion in concrete and corrosion of rebars have been investigated. Effect of parameters such as cement, water to binder ratio, slump, aggregates, and characteristic compressive strength are analyzed using response surface method (RSM). Regression analysis is used to evaluate the electrical resistivity related with each concrete mixture. Subsequently, the corrosion rate is obtained by using the electrical resistivity and chloride migration coefficient. To validate the regression analysis and investigate the effect of rebar corrosion on the flexural behavior of the beam, a finite element software is employed. Corrosion is applied to a selected beam and the load-displacement plots are obtained by analyzing four laboratory samples. The plots show good agreement between numerical and experimental results. Also, the effect of changing only one parameter is observed on the flexural capacity of the selected beam and its life cycle. It is observed that increasing the water to binder ratio, aggregate content, and slump, decrease the flexural capacity of the beam, while increasing the cement content and characteristic compressive strength leads to a positive effect on flexural capacity.

Characteristics of metakaolin-based geopolymer concrete for different mix design parameters

Geopolymer is emerging as a potential alternative material to the ordinary Portland cement (OPC) owing to its energy efficiency and environmental protection. However, the effect of the mix design parameters on the behavior of geopolymer concrete (GPC) produced using local metakaolin (MK) is not well established. This paper presents findings from a comprehensive experimental program to study the effect of various mix design parameters on the properties of fresh and hardened MK-based GPC. Seventeen mixes were cast in four groups to investigate the effect of four parameters, including sodium silicate to sodium hydroxide ratio, alkaline solids to MK ratio, aggregate content, and water to solids ratio on the properties of GPC. The investigated properties included workability, density (wet and dry), development of compressive strength with age, splitting tensile strength, ultrasonic pulse velocity, water absorption, and horizontal abrasion resistance. Besides, two reference OPC concrete mixes, equivalent to two MK-based geopolymer mixes, were tested for the sake of comparison. The test results were helpful in developing a better understanding of the behavior of MK-based GPC. Some useful models are proposed for predicting workability, splitting tensile strength, water absorption, and weight loss in abrasion for MK-based GPC. The test results were supplemented and confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analysis performed on some selected GPC mixes.

Effects of Compositional and Physico – Chemical Mix Design Parameters on Properties of Fly Ash Geopolymer Mortars

The present experimental study investigated the effects of mix design parameters on workability and compressive strength of fly ash geopolymer (FA – GPC) mortars. Observed effects of the compositional parameters comprising SiO2/FA, Na2O/FA and H2O/FA mass ratios, were inter – linked with those of the physico – chemical mix parameters namely:– the concentration of sodium hydroxide solution, ratio of sodium silicate to sodium hydroxide, and the alkali activator to raw material ratio. In the preparation of mortars, low calcium (Class F) FA was activated using a combined solution of sodium hydroxide and sodium silicate, and mixed with fine aggregate at the aggregate to FA ratio of 2.25. Altogether, seventy – two (72) mortar mixtures were prepared by varying the values of compositional parameters. It was found that the SiO2/FA ratio of 0.08 to 0.11, Na2O/FA ratio of 0.05 to 0.08, and H2O/FA ratio of 0.32 to 0.37, are the optimum ranges that gave the best workability values and compressive strength results, depending on the H2O/FA ratio. In mix design, the various values of compositional parameters are obtained by appropriately combining the aforementioned physico – chemical parameters.

Effects of mix design parameters on heat of geopolymerization, set time, and compressive strength of high calcium fly ash geopolymer

In this study, the effects of key design parameters, such as SiO2/Na2O mole module (Module), concentration of solute in alkaline solution (Concentration), liquid-to-fly ash mass ratio (L/F), and curing temperature on the geopolymerization process, set time, and compressive strength of high calcium fly ash geopolymer mixes were investigated. The geopolymerization process of these mixes was monitored using a semi-isothermal calorimeter at testing temperatures of 23 °C and 50 °C for 24 h. The results showed two major exothermic peaks generated during the fly ash geopolymerization processes. The first peak, the dissolution peak, appeared within the first hour after the fly ash was in contact with a liquid activator, and it did not vary very much with mix design parameters, while the second peak, the polymerization peak, varied largely in its amount and emerging time with mix design parameters of the geopolymers. As Module increased, the set time was accelerated but the total heat generated from geopolymerization and the compressive strength of the geopolymer were reduced. As Concentration increased, the set time for mixes with 1.0 and 1.5 Module prolonged but it was shortened for the mixes with 2.0 Module, while the total heat of geopolymerization and strength of these mixes were increased. Elevated curing temperature decreased the polymerization peak time, increased the total heat of geopolymerization, and improved the strength of the geopolymers. Additionally, the close relationships between the calorimetric characterization and setting time/compressive strength were obtained. To achieve optimal strength and setting behavior, it is recommended that a geopolymer mix made with high calcium fly ash shall be designed to have an activator with Modules ≤ 1.5, Concentrations of 20–25%, and L/F ≤ 0.40, and elevated curing (e.g., at 50 °C) is preferred.

Analyzing and Predicting Permeability Coefficient of Roller-Compacted Concrete (RCC)

The permeability of roller-compacted concrete (RCC) substantially affects its functionality and safety. This study investigates the effect of mix design parameters on the performance of RCC. For this purpose, approximately 500 laboratory specimens were prepared and tested. A formula and an artificial neural network (ANN) were proposed to predict the permeability coefficient of RCC by considering the main parameters, which were then verified independently using new specimens. Furthermore, the experimental data were analyzed by the Taguchi method and analysis of variance (ANOVA) to evaluate the level of parameter contribution. Based on the results, the permeability coefficient was highly dependent on the mix design and strength of the RCC specimens. The ANN model can predict the permeability coefficient of RCC more accurately than the proposed formula. The statistical analyses revealed that the water-to-cement ratio had the highest effect on the permeability coefficient and the mechanical properties. The findings of this investigation indicated valuable information regarding cost and time savings as well as eliminated laboratory trial and error in designing RCC structures.

Influence of mix design parameters on asphalt concrete aging rate using I-FIT specimens

Aging is considered an important factor contributing to the deterioration of asphalt concrete (AC) pavements. As a result of aging, the resistance of AC pavements to various forms of cracking including fatigue, thermal, or block is reduced. Therefore, it is critical to understand the effect of aging on AC pavement cracking development and identify the effect of AC mix design parameters on the aging rate. A wide range of AC surface mixes was investigated in this study using the Illinois Flexibility Index Test (I-FIT) after the specimens were subjected to various lab-simulated aging conditions. The flexibility index (FI), an I-FIT outcome parameter, decreases consistently after long-term aging. This effect is primarily due to changes in the post-peak slope, which represents crack growth rate. The effect of mix design parameters on FI deduction rate (or aging rate) was analyzed using statistical methods. Single and multiple linear regression techniques were implemented to identify the significant of AC mix design parameters on the aging rate. The effect of voids in mineral aggregate (VMA), low-temperature true grade, asphalt binder replacement (ABR), mix type, and effective asphalt content was found to be significant. The increase of ABR, effective asphalt content, and VMA, and/or a decrease of low-temperature true grade induce a decrease in the aging rate of AC.

Mix Design and Recycled Aggregates Effects on the Concrete’s Properties

An experimental program was carried out to study the properties of concretes with C25/30 and C35/45 resistance classes designed using natural aggregates and recycled ones provided from construction and demolition waste (C&DW). Eight mixtures were prepared with different incorporation ratios of fine and coarse recycled aggregates. The physical and mechanical characteristics were measured and their evolution regarding to the paste volume, the equivalent replacement ratio and the quality of the interface between recycled aggregates and new paste has been investigated. Scanning Electron Microscopic observations have revealed a good quality of the interface. It was found that water porosity is more dependent on the equivalent replacement ratio than on the volume of the new paste. The same conclusions are reported for the electrical resistivity which has been related to the water porosity. Based on experimental results, it has been found that the Archie’s law predicts the electrical resistivity as a function of water porosity for all type of concrete. The effect of mix design parameters and aggregates properties on the compressive strength has been investigated and a model is proposed on the basis of Feret’s expression through experimental results and data points available in the literature. The modified expression is related to the aggregate fragmentation resistance expressed by the Los Angeles coefficient (LA). The Feret’s coefficient can be taken equal to 6.4 if LA ≤ 20% and it is inversely proportional to LA otherwise. With regard to the splitting tensile strength, it can be correlated to the electrical resistivity through a power law relationship. The elastic modulus, the peak and the ultimate strains are than rewritten as functions of the compressive strength and the replacement ratio to model the full stress–strain curve under uniaxial compression. Furthermore, the validity of using EC2 to model the evolution of all mechanical properties with age is ensured.

Effects of mix design parameters and rheological properties on dynamic stability of self-consolidating concrete

Stability is a crucial property for successful placement and performance of self-consolidating concrete (SCC). Dynamic stability refers to the segregation resistance of concrete during flow and is not thoroughly described in literature to date. In this research, a newly developed dynamic stability test, the Tilting-box test, was employed to evaluate the effect of different mix design parameters on the dynamic segregation of SCC. Paste volume, water-to-binder ratio (w/b), maximum size of aggregate (MSA), aggregate density, and aggregate grain-size distribution were shown to affect the dynamic stability of SCC, while the coarse aggregate shape did not have a significant influence. The slump flow and V-funnel flow time as well as the rheological parameters were found to be an efficient tool for controlling dynamic segregation. Higher yield stress or plastic viscosity reduced the risk of dynamic segregation. Recommended workability characteristics and rheological parameters of SCC to ensure adequate dynamic stability level were proposed.

Mechanical and thermal characterisation of geopolymers based on silicate-activated metakaolin/slag blends

This article assesses the effect of mix design parameters on the compressive strength and thermal performance of alkali silicate-activated blends of metakaolin (MK) and granulated blast furnace slag (GBFS). A strong interrelationship between the effects of activator composition and the GBFS/(GBFS + MK) ratio is identified through statistical analysis of compressive strength data. Pastes formulated with higher SiO2/Al2O3 molar ratios show improvements in mechanical strength with increasing GBFS addition, associated with the formation of a structure comprising coexisting aluminosilicate ‘geopolymer’ gel and Ca-rich Al-substituted silicate hydrate (C-(A)-S-H) reaction products. The inclusion of GBFS in MK-based geopolymers seems also to improve their performance when exposed to high temperatures, as higher residual compressive strengths are reported for these mixtures compared to solely MK-based systems. Only slight differences in shrinkage behaviour are observed at temperatures of up to 600 °C with the inclusion of GBFS; however, slag-blended pastes exhibit enhanced stability at temperatures exceeding 800 °C, as no variation in the compressive strength and no additional shrinkage are identified. These results suggest that nanostructural modifications are induced in the gel by the inclusion of GBFS into MK-based geopolymers, improving the overall performance of these materials.

Identification of microstructural characteristics in lightweight aggregate concretes by micromechanical modelling including the interfacial transition zone (ITZ)

An approach which combines both experimental techniques and micromechanical modelling is developed in order to characterise the elastic behaviour of lightweight aggregate concretes (LWAC). More than three hundred LWAC specimens with various lightweight aggregate types (5) of several volume ratios and three different mortar matrices (normal, HP, VHP) are tested. The modelling is based on iterative homogenisation process and includes the ITZ specificities experimentally observed with scanning electron microscopy (SEM). In agreement with experimental measurements, the effects of mix design parameters as well as of the interfacial transition zone (ITZ) on concrete mechanical performances are quantitatively analysed. Confrontations with experimental results allow identifying the elastic moduli of LWA which are difficult to determine experimentally. Whereas the traditional empirical formulas are not sufficiently precise, predictions of LWAC elastic behaviours computed with the micromechanical models appear in good agreement with experimental measurements.

An updated look at drying shrinkage of Portland and blended Portland cement concretes

National and overseas reports clearly show that a significant proportion of concrete construction problems are associated with drying shrinkage. These results could be a result of few available long-term drying shrinkage data and changes of the behaviour of concrete mixes used nowadays. Therefore, poor estimates of drying shrinkage strains from prediction models could impair the performance and service life of concrete structures. The objective of the current research was to analyse the effect of mix design parameters on drying shrinkage of concretes made with Portland and blended Portland cements, considering 30 mixes that are commonly used in local construction, tested up to 1350 days of drying. It was concluded that, when using rapid-hardening cement of any type, a larger maximum aggregate size and lower water content reduces drying shrinkage. Cement and aggregate type are shown to have a significant effect on drying shrinkage time function and magnitude. Experimental results were compared with calculated drying shrinkage strains estimated by ACI 209, CEB MC90, B3, GL 2000, Sakata 1993 and Sakata 2001 models. It was concluded that none of the shrinkage prediction models adequately reproduced the observed shrinkage behaviour of concrete made with Chilean Portland and blended Portland cements, underestimating the actual long-term drying shrinkage strains.