Superplasticizer Dosage Research Articles

Effects of modified binders on flowability of grout and properties of preplaced aggregate concrete

In preplaced aggregate concrete (PAC), it is important yet complex to achieve a grout with high flowability and bleed resistance simultaneously. Supplementary cementitious materials, typically incorporated to impart desired properties to concrete and to complement economic and environmental benefits, may uniquely alter the properties of PAC to that of conventional concrete. Therefore, comprehensive knowledge of incorporating supplementary cementitious materials, considering alterations in their flowability and constituent materials to improve the overall performance of PAC is essential. The present study investigates the properties of PAC, incorporating ground granulated blast furnace slag (GGBS) and silica fume (SF) as partial replacement of cement at 0–40% and 0–10%, respectively. Different proportions of GGBS and SF were considered, where, flowability and superplasticizer dosage were varied with and without incorporating sand. Grout properties were evaluated in terms of flowability and compressive strength and PAC properties were evaluated in terms of mechanical strength, durability, and dimensional stability. The findings revealed that the combination of GGBS and SF in grout displayed suitable flowability and acceptable strength. Removal of sand from grout improved the properties of grout while deteriorating the properties of PAC. PAC produced using grout with 10% SF and sand to binder ratio of 0.5, exhibiting efflux time of less than 20 s, displayed the highest compressive strength. GGBS and SF significantly improved chloride ion penetration of PAC with the drawback of increased drying shrinkage. Nevertheless, all PAC mixes could still be classified as low shrinkage concrete. PAC produced with 40% GGBS and 10% SF exhibited comparable compressive strength and enhanced resistance to chloride ion penetration to that of PAC without GGBS/SF.

Effect of dosage of superplasticizer on earth concrete

The environmental load put forth by the construction industry is tremendous. Being a major contributor to the present-day environmental situation, the construction industry must embrace the necessary changes. Sustainable development, effective utilization of resources and responsible engineering are of utmost priority. There are several alternative construction materials on the rise, adhering to such new requirements, in addition to the benefits of the materials that are already being employed. Earth concrete is one such emerging construction material. In earth concrete soil along with other constituents are made into a flowable form that can be cast into various shapes using forms and cured to attain certain desired strength characteristics. Binders, coarse aggregates and admixtures for earth concrete are selected on the basis of the characteristic requirements of the resulting matrix. In the present study, laterite soil is used to produce earth concrete, cement acts as binder, crushed stone as coarse aggregate and a naphthalene-based admixture helps in achieving the required workability characteristics. By the incorporation of Ceraplast 300, a naphthalene-based super plasticizer, the density, workability and the compressive strength of earth concrete have been enhanced. The paper considers the effect of dosage of super plasticizer on the workability, density and strength characteristics of earth concrete. Through parametric experimental study of earth concrete specimens, the optimum dosage of the naphthalene based super plasticizer has been determined. 1 % dosage of the super plasticizer with earth concrete exhibited the best results for the selected matrix. In the experimental program, earth concrete capable of sustaining 47.7 MPa stress at failure was achieved, which accentuates the possibilities and need for further studies on earth concrete.

Mix-Design Optimization of Self-Compacting Paste Incorporating Powdery Industrial Solid Wastes Based on a Paste Rheological Threshold Theory

The effect of powdery industrial solid wastes on the optimal proportion of pastes and self-compacting concrete (SCC) is investigated in this study. There were nine groups of powdery industrial solid wastes designed, including cement, fly ash (FA), limestone powder (LP), granulated blast furnace slag (GBFS), and modified phosphogypsum (MPG). The powder materials have different properties, such as zeta potential, density, and specific surface area. The paste rheological threshold theory was used to calculate the self-compacting paste (SCP) zone and the optimal proportion. To assess the effect of powder properties on the optimal mix proportion, a model was proposed. The linear regression method was used to obtain quantitative relationships between the optimal proportion and powder characteristics, which can benefit in the SCC optimization process. A new powder combination was designed, and the optimal water-to-powder ratio by volume (VW/VP) and the dosage of superplasticizer by mass (SP%) can be calculated using the powder combination’s physical and chemical properties. The search area was narrowed, and the SCP zone was obtained, where a good SCC was achieved, validating the powder effect model’s effectiveness.

Influence of limestone calcined clay cement on properties of 3D printed concrete for sustainable construction

The research on emerging digital construction techniques, particularly the 3D concrete printing of cement-based materials, is imperative owing to the several economic, environmental, and societal benefits it offers over conventional cast-in-place concrete. In this study, limestone calcined clay cement (LC3) was utilised for 3D printed concrete (3DPC) production towards sustainable composite infrastructure by replacing up to 50% of ordinary Portland cement (OPC) with limestone and calcined clay (LC2). The fresh, rheological, and hardened mechanical properties of fibre-reinforced 3DPC were investigated. Six different 3DPC mixes were made for these purposes: the control (no LC2), four mixes with 1.0, 0.91, 0.8, and 0.6% superplasticiser (SP) dosages, and the last mix without micro-synthetic polypropylene fibre. Findings revealed that achieving a slump of less than 10 mm and a slump flow between 140 and 160 mm as required by relevant standards (ASTM C1437 & C230/C230 M) is crucial in obtaining an extrudable 3D concrete mixture. A finite flow value and satisfactory rheological properties are achieved in mixes C (with 0.6 SP), D (0.8 SP), and Dadj (0.91 SP) to produce a feasible 3D printable cement-based concrete mixture. Test results validated the promise of LC2 as a partial replacement for OPC in digital concrete depending on the testing orientations of the printed samples. Buildability performance using a gantry-type 3D printer was conducted and the significant orthotropic phenomenon was indicated in the compressive properties of printed samples. The presence of fibres toughened the cylindrical strength perpendicular to the layer-interface-plane and enhanced the bearing load in tension and flexure, thereby making the direction 1 (D1) interfacial flexural/tensile bearing capacity comparable to cast-in-situ 3DPC samples.

Multi-criterion optimization of Low-Cost, Self-compacted and Eco-Friendly Micro-calcium-carbonate- and Waste-glass-flour-based Ultrahigh-Performance concrete

This paper provides a multi-objective optimization approach to designing and manufacturing ultra-high-performance concrete (UHPC) with low cement content. Micro calcium carbonate and ground waste glass were employed as partial substitutes for cement and microsilica (MS) to achieve this goal. A three-factor design of experiments was used to achieve the most desirable rheological and mechanical properties with minimal quantities of cement and MS. In this context, the cement dosage (factor A), water-to-binder ratio (factor B), and superplasticizer dosage (factor C) were taken into account. By utilizing Andreasen & Andersen's (MAA) particle packing theory, dense particle packing was achieved throughout the experimental design. Regression models were developed to simulate the time-dependent rheological and mechanical properties of the UHPC. It was observed that the mathematical optimization was valid experimentally with reduced absolute deviations between 0.22 % and 1.23 % for slump flow and 3.49 % to 4.62 % for compressive strength at 28 days. The study showed that approximately 590 kg/m3 of cement would be most effective for recycled glass UHPC mixes. The proposed design will likely produce a compressive strength exceeding 150 MPa with satisfactory rheological properties at a lower cost.

Investigation of the performance of basic magnesium sulfate cement mortar

Basic magnesium sulfate cement (BMSC) is a kind of magnesium oxide (MgO)–magnesium sulfate (MgSO4)–water (H2O) modified ternary cementitious material prepared from light burned magnesia, magnesium sulfate heptahydrate, water and additives. The effects of α-magnesium oxide/magnesium sulfate ratio (MO/MS), water/magnesium sulfate ratio (W/MS), sand-to-binder ratio (s/b) and superplasticiser dosage (SPD) on the performance of BMSC mortar were studied for the first time in this work. The results showed that for, optimal 28-day flexural strength, α-MO/MS = 10:1, W/MS = 16:1, s/b = 0.8 and SPD = 0.3%. For optimal 28-day compressive strength, α-MO/MS = 8:1, W/MS = 14:1, s/b = 0.6 and SPD = 0.4%. For best water resistance, α-MO/MS = 12.5:1, W/MS = 14:1, s/b = 0.2 and SPD = 0.1%. Based on these results, the basic mix proportion ranges of BMSC mortar should be α-MO/MS = 8:1–12.5:1, W/MS = 14:1–16:1, s/b = 0.2–0.6 and SPD = 0.1–0.4%.

Optimisation of Mix Proportion of 3D Printable Mortar Based on Rheological Properties and Material Strength Using Factorial Design of Experiment

In the production of 3D printable mortar (3DPM), numerous efforts have been made globally to effectively utilise various cementitious materials, admixtures, and fibres. The determination of rheological and material strength properties is crucial for successful 3D concrete printing because the materials used in 3DPM must possess the unique characteristic of making mortar flowable while being strong enough to support the weight of subsequent layers in both fresh and hardened states. The complexity of the required characteristics makes it challenging to develop an optimised mix composition that satisfies both the rheological and material strength requirements, given the wide range of available admixtures, supplementary cementitious materials, and fibres. Fly ash, basalt fibre and superplasticiser when blended with cement can help to improve the overall performance of 3DPM. The objective of this research is to optimise the rheological properties and material strength of 3D printable mortars (3DPM) containing cement, fly ash, basalt fibre, and superplasticiser. This study aims to produce 3DPM with an optimised mix composition to meet the requirements of both rheological and material strength characteristics using the factorial design approach and desirability function. Different dosages of cement, fly ash, basalt fibre, and superplasticiser are chosen as the primary design parameters to develop statistical models for the responses of rheological and material strength properties at 7 and 28 days. The results expressed in terms of the measured properties are valid for mortars made with cement ranging from 550 to 650 kg/m3, fly ash from 5% to 20% (of cement), superplasticiser from 2 to 4 kg/m3, and basalt fibre from 1 to 3 kg/m3. The rheological properties are evaluated using slump flow, cone penetrometer, and cylindrical slump tests, while the mechanical strength is evaluated using a three-point bending test and compressive test. A full factorial design experiment (FoE) is used to determine the significant parameters effecting the measured properties. Prediction models are developed to express the measured properties in terms of the primary parameters. The influence of cement, fly ash, basalt fibre, and superplasticiser is analysed using polynomial regression to determine the main effects and interactions of these primary parameters on the measured properties. The results show that the regression models established by the factorial design approach are effective and can accurately predict the performance of 3DPM. Cement, fly ash, and superplasticiser dosages have significant effects on the rheological and mechanical properties of mortar, while basalt fibre is able to influence the static yield stress and flexural strength of 3DPM. The utilisation of regression models and isoresponse curves allows for the identification of significant trends and provides valuable insight into the behaviour of the material, while desirability function is useful to optimise overall performance of mix proportions to meet the desired performance objective at fresh and hardened states.

Combined effect on properties and durability performance of nanomodified basalt fiber blended with bottom ash-based cement concrete: ANOVA evaluation

A control of a cement composite structure formation from modern positions should be carried out taking into account the synergistic effect of its components. The goal of the article is to study the combined effect of nanomodified basalt fiber (NBF) and bottom ash (BA) as structural elements of concrete using a two-factor analysis of variance ANOVA. The tasks for achieving this goal are the development of nanomodified basalt fiber bottom ash-cement concretes, as well as the study of their fresh, physical and mechanical properties (slump, slump flow, average density, compressive and flexural strength, elastic modulus and crack resistance) and durability performances (water, frost, and abrasion resistance). Nanomodified basalt-fiber-reinforced concretes (from 0 to 7 wt % NBF) have been developed, in which the economical Portland cement CEM I 32.5 N is replaced by up to 45 wt % mechanically activated bottom ash (400 m2/kg). Achieving uniform flowability of the compositions (slump 20–22 cm and slump flow 45–52 cm) was carried out by varying the dosage of an economical superplasticizer with a high water-reducing ability (35%). The joint effect of the BA and NBF provides control over the structure formation of cement materials, which ensures the redistribution of internal stresses from shrinkage deformations throughout the entire volume of the composite; during loading, the process of crack formation is retarded, stress concentration near structural defects is reduced, and stresses are redistributed in the microstructure of the cement composite between its components.High values of mechanical properties (compressive strength up to 59.2 MPa, flexural strength up to 17.8 MPa, elastic modulus up to 52.6 GPa, limit stress intensity factor 0.507 MPa m0.5) are explained by the complex effect of bottom ash and nanomodified basalt fibers. For the composition with 30 wt % BA and 5 wt % NBF, W18 water resistance grade, F400 frost resistance grade, and the abrasion resistance of 0.59 g/cm2 were achieved, which characterizes the high durability of the developed materials.

Study on Influencing Factors of Paste Coating Thickness of Pervious Concrete

Pervious concrete (PC) is a multifunctional material with good water permeability, noise reduction, and heat absorption properties. The most critical performance indicators of the PC are permeability and strength, which are mainly affected by the cement paste coating thickness (PCT) on the aggregate surface. The experiment was carried out to study the influence of the water–cement ratio, superplasticizer dosage, aggregate roughness, and aggregate size on PCT, and a new normalization method was proposed for grey correlation analysis to determine the influence degree of the above factors on PCT. Finally, fitting models for predicting the PCT were established based on experimental data. The experimental results indicate that the influence of the water–cement ratio on PCT can be divided into two stages, whereby the PCT shows a slow decline and then a rapid decline with the increase in water–cement ratio; with the increase in superplasticizer dosage, the PCT represents an exponentially decreasing trend; the PCT increases with the aggregate size and aggregate roughness. Based on the grey correlation analysis, the superplasticizer dosage exerts the greatest influence on PCT, followed by the water–cement ratio, aggregate size, and aggregate roughness. The results of this study revealed the change law of PCT under the action of the above factors, which established the premise of controlling the strength and permeability of PC from the perspective of the PCT and provided a reference for the mixture proportion design.

Performance of cement mortar modified with GGBFS at elevated temperatures with various w/b ratios and superplasticizer dosages

The present research aimed to evaluate and analyze the performance of Portland cement mortars that were heated to a maximum temperature of 625 °C and contained various amounts of GGBFS, superplasticizer, and water-to-binder ratios. Because of the enormous temperatures they generate, fires have the potential to cause structures made of concrete to collapse. In order to anticipate concrete buildings structural safety in the event of specific accidents or specific service conditions, it’s important to consider their behavior under exposure to elevated temperatures. The findings of the tests showed that greater exposure to heat and greater w/b ratios caused greater weight loss. The highest compressive strength for mixes containing GGBFS was found at a temperature of 225 °C, but the compressive strength of mixes without GGBFS decreased with increasing the temperature. The flexural strength was proportional with increasing the temperature to 225 °C and declined with a further increase to 625 °C for mixes with no GGBFS at 0.4 w/b, while for mixes containing GGBFS, the flexural strength decreased with higher temperature. In general, at 0.4 and 0.48 w/b ratios, higher flexural strength was observed for all mixes with elevating the exposure temperature to 225 °C, followed by the flexural strength decreasing at 625 °C temperature. The splitting tensile at all w/b ratios was enhanced with an exposure temperature of 225 °C and degraded at 625 °C. Finally, SEM microstructural analysis results indicated that increasing exposed temperature loosens the matrix's microstructure, creating larger microcracks and pores.

Valorization of ceramic waste powder as cementitious blend in self-compacting concrete – A review

The ceramic waste (CW) produced from ceramic industries is dumped as landfills creating pollution. Many researchers have worked in evaluating the pozzolanic potential of CW. Most authors have found that CW contains high amount of Silica and Alumina like other natural pozzolans and can be effectively used to replace cement. The pozzolanic potential of CW can be very useful especially in self-compacting concrete, where the powder requirement is comparatively high. The use of CW to replace cement helps in the utility of industrial wastes and in maintaining the ecological balance thus reducing the consumption of cement. Thus, this paper reviews the use of CW in self-compacting concrete. For this purpose, design parameters like water to binder ratio (w/b), water to cement ratio (w/c), superplasticizer dosage (SP) (kg/m3) and replacement percentage of ceramic waste are studied on the slump flow and compressive strength of SCC with CW have been selected. It is observed that with respect to different grades of SCC, designed parameters affects the fresh and strength properties of SCC.

Mechanical Activation of OPC for Lower Strength UHPC with Reduced Silica Fume Content

Ultra-High-Performance Concrete (UHPC) traditionally exhibits compressive strength exceeding 150 MPa. However, variants have been identified with slightly lesser strengths that still surpass those of standard concrete; these are termed Lower Strength Ultra-High-Performance Concrete (LSUHPC). This study focused on the strategic utilization of Ordinary Portland Cement (OPC) in LSUHPC formulation while significantly curtailing the extensive use of silica fume, which is a common practice in UHPC production. Typically, high-performance concrete, with strengths ranging from 120-150 MPa, is produced using fine aggregates, heavy doses of silica fume, superplasticizer, and fiber. Contrary to this traditional method, our research developed an LSUHPC mix design with a significantly reduced volume of silica fume. For the current research stage, the use of steel fiber was omitted. To counteract the reduction in silica fume, the OPC was subjected to mechanical grinding to enhance its particle fineness and reactivity. Additionally, a low volume of class F fly ash was incorporated into the mixture to improve its workability. This adjustment was theorized to diminish inter-particle voids, reduce the water requirement, and increase the mixture’s density. With a fixed superplasticizer dosage of 4%, the aim was to minimize the water-to-binder ratio, maintaining workability and achieving enhanced particle packing and compressive strength. Following a series of grinding, particle fineness analyses, mix design formulations, and consistency tests, it was confirmed that the strategic application of OPC, combined with fly ash and reduced silica fume levels in the LSUHPC formulation, can achieve the targeted high compressive strength. This approach opens the door for cost-efficient LSUHPC production by drastically reducing the use of silica fume.

Influence of Raw Kaolin Clay and Its Dehydroxylated Form on The Properties and Performance of Portland Cement Mortar

Kaolin, also known as China clay, is one of the materials that can be used as partial replacement for Portland cement but most of the research has been focused on its dehydroxylated form (metakaolin). The lack of interest in raw kaolin clay as a cement replacement material is partly due to its negative impact on strength and the traditional perception that raw clay is detrimental to concrete. However, the use of raw kaolin clay as cement replacement may offer other benefits, such as energy saving and the potential to produce durable cement-based material at low cost. Therefore, this paper presents findings on the influence of raw kaolin clay on the properties and durability performance of Portland cement mortar in comparison with metakaolin, when used as partial substitute. The results show that the use of raw kaolin clay as a partial substitute for Portland cement improved all aspects of the durability properties investigated, which became more apparent with age. Despite having the lowest compressive strength, the raw kaolin clay mix displayed a lower porosity, better resistance to water absorption and finer pores than the control. In contrast to the raw kaolin clay, the metakaolin significantly enhanced both strength and durability. The results also reveal that at a given superplasticizer dosage and replacement level, the kaolin and metakaolin mixes exhibited the same consistency in the fresh state and a similar range of pore size distribution and total intrusion volume at 28 days. The findings further demonstrate that raw kaolin clay can be used as Portland cement replacement material to produce durable mortar and concrete, particularly for applications that do not require high strength.

Compressive Strength Estimation of Waste Marble Powder Incorporated Concrete Using Regression Modelling

A tremendous volumetric increase in waste marble powder as industrial waste has recently resulted in high environmental concerns of water, soil and air pollution. In this paper, we exploit the capabilities of machine learning to compressive strength prediction of concrete incorporating waste marble powder for future use. Experimentation has been carried out using different compositions of waste marble powder in concrete and varying water binder ratios of 0.35, 0.40 and 0.45 for the analysis. Effect of different dosages of superplasticizer has also been considered. In this paper, different regression algorithms to analyse the effect of waste marble powder on concrete, viz., multiple linear regression, K-nearest neighbour, support vector regression, decision tree, random forest, extra trees and gradient boosting, have been exploited and their efficacies have been compared using various statistical metrics. Experiments reveal random forest as the best model for compressive strength prediction with an R2 value of 0.926 and mean absolute error of 1.608. Further, shapley additive explanations and variance inflation factor analysis showcase the capabilities of the best achieved regression model in optimizing the use of marble powder as partial replacement of cement in concrete.

Contribution to low-carbon cement studies: Effects of silica fume, fly ash, sugarcane bagasse ash and acai stone ash incorporation in quaternary blended limestone-calcined clay cement concretes

Nearly 10% of global carbon dioxide (CO2) emissions come from Portland cement production, in turn exacerbating the Greenhouse Effect. Consequently, the development of alternative materials to mitigate this adverse environmental impact is essential. Limestone-Calcined Clay Cement (LC³) is presented in academic literature as an alternative for reducing CO2 levels from the cement industry without significant modifications in concrete properties. However, the use of wastes from other industries – known as supplementary cementitious materials (SCMs) – in LC³ mixtures should be investigated due to the interaction between SCMs and calcined clays. This study evaluated the properties of Limestone-Calcined Clay Cement Concretes containing different SCMs, namely silica fume, fly ash, sugarcane bagasse ash and acai stone ash, in fresh and hardened states, as well as its durability. Slump, compressive and splitting tests, carbonation and volumetric electrical resistivity analyses, Thermogravimetric Analysis (TGA), Energy Dispersive X-Ray Spectroscopy (EDS), X-Ray Fluorescence (XRF) and Scanning Electron Microscopy (SEM) images were performed in this study. Results showed that high superplasticizer dosages are required in LC³ in order to obtain workable concretes independent of SCMs presence. A competition between SCMs and calcined clay for the portlandite consumption in pozzolanic reactions was noted, reducing compressive strength between 20% and 45% of LC³ mixtures. TGA analysis showed that all portlandite was consumed, mainly by the pozzolanic reactions from calcined clay. The presence of SCM in LC³ concretes increased the electrical resistivity up to 48%. However, all LC³ concretes presented higher carbonation fronts compared to the reference Portland cement concrete due to the low availability of calcium to react with CO2 that penetrates through concrete pores. Among the SCMs, silica fume, fly ash and sugarcane bagasse ash presented a suitable performance to use in LC³ mixture. However, LC³ silica fume concretes presented the best global performance considering concrete properties in fresh and hardened state, as well as its durability.

On the “Thixotropic” Behavior of Fresh Cement Pastes

Thixotropic behavior describes a time-dependent rheological behavior characterized by reversible changes. Fresh cementitious materials often require thixotropic behavior to ensure sufficient workability and proper casting without vibration. Non-thixotropic behavior induces a workability loss. Cementitious materials cannot be considered as an ideal thixotropic material due to cement hydration, which leads to irreversible changes. However, in some cases, cement paste may demonstrate thixotropic behavior during the dormant period of cement hydration. The aim of this work is to propose an approach able to quantify the contribution of cement hydration during the dormant period and to examine the conditions under which the cement paste may display thixotropic behavior. The proposed approach consists of a succession of stress growth procedures that allow the static yield stress to be measured. For an inert material, such as a calcite suspension, the structural build-up is due to the flocculation induced by attractive Van der Waals forces. This structural build-up is reversible. For cement paste, there is a significant increase in the static yield stress due to cement hydration. The addition of superplasticizer allows the thixotropic behavior to be maintained during the first hours due to its retarding effect. However, an increase in the superplasticizer dosage leads to a decrease in the magnitude of the Van der Waals forces, which can erase the thixotropic behavior.

Designing Self-Compacting Concrete Using Local Materials from the Arid Region of Adrar, Algeria

Abstract In the construction sector, the non-renewable world resource of sand is largely used to produce mortar and concrete. It has been estimated that over 10 billion tons of sand have been produced, with 1.2 billion tons used in concrete over the last decade, which leads to a progressive reduction of available construction materials and environmental impacts. Since desert sand resources are abundant in arid region of Adrar (Southern Algeria), it would be viable to use desert-sand as an alternative material for the production of self-compacting concrete. Therefore, self-compacting concrete is experiencing significant demand in that arid region since it offers socio-technical and economic solutions to stakeholders in the construction and public works industry. Furthermore, the present study aims to address the concerns of these stakeholders. The results obtained showed that the self-compacting concrete that was made with local materials, behave correctly, both in the fresh and hardened states. This concrete included a 1% super plasticizer dosage, a gravel-to-sand (G/S) ratio varying between 0.8 and 1.1, and additions of limestone fillers up to 50% relative to the mass of cement for self-compacting concrete made with dune sand, while this percentage could go up to 38% for self-compacting concrete made with corrected sand (63% crushed sand with 37% dune sand).

Effect of water to binder ratio, polycarboxylate superplasticizer and metakaolin dosages on rheological and viscoelastic properties of fresh metakaolin-air lime pastes

As an ancient architectural restoration material, hydraulic lime has good early properties, which is necessary to ensure its successful application. Metakaolin-air lime (MK-AL) composite material as a kind of hydraulic lime, the initial fluidity, macroscopic rheological properties, viscoelasticity and dissolution-early hydration are systematically investigated by setting different water to binder (w/b) ratios, polycarboxylate superplasticizer (SP) and metakaolin dosages. The results showed that the initial fluidity of MK-AL pastes has a more obvious improvement by adding SP. The rheological behavior of MK-AL paste was well characterized by both the Bingham model and H–B model. The reduction of yield stress and plastic viscosity on account of the better dispersion of particles in MK-AL paste. The rheological behavior expresses shear thickening without SP and shear thinning with SP in MK-AL paste are revealed. The viscoelastic transformation is illustrated by the macroscopic viscosity index, elastic index, storage modulus, loss modulus, solid-liquid balance and fluidity index parameters, these parameters have a reduction to a large degree with increasing w/b ratios and SP dosage, while the variation of metakaolin dosage has relatively little impact. The increase in w/b ratio and SP dosage promote the dispersion and dissolution of the particles in the aqueous solution, and the strong dispersive capacity delays the process that particles heap up rapidly and network structure formation in MK-AL pastes. Furthermore, the exothermic rate of the two hydration stages is reduced significantly, as well as the appearance of the exothermic peak of hydration is delayed.

Dilatancy swerve in superplasticized cement powder paste

Superplasticizer (SP), particularly poly-carboxylate based, can improve substantially the strength-workability limits of cement powder paste by decreasing the water demand for hydration. It however brings unfavourable effect of dilatancy which is the increased viscosity at high shear flow that impairs the pumpable distance and mixing uniformity. The dilatancy in cement powder paste was caused by the clustering of mobile and adsorbed polymers in SP that forms dead zone of flow and increase flow impedance. Previous research revealed that the dilatancy increased as SP dosage increased. Nevertheless, this study found that it does not increase monotonically as the SP dosage increases. It increases initially due to the introduction of SP but decreases after reaching the “critical SP dosage”. It is because adequate SP disperses effectively the cement particles for better hydration which decrease the interstitial void hence mobile SP polymers. This phenomenon is referred to “dilatancy swerve”, the understanding of which is essential in designing practical mortar or concrete mix to mitigate the impact of increased viscosity in pumping and mixing. To investigate the factors affecting the critical SP dosage, this study tested the dilatancy of various types of cement powder paste that consist of cement, fly ash (FA), silica fume (SF) and/or limestone (LS). It was found that the critical SP dosage decreased as FA was used to substitute an equal volume of cement but increased as SF or LS was used. Lastly, the general trend of decreasing dilatancy as WPD increased was observed.

Comparing Permeability and Drying Shrinkage of the Concrete Containing Mineral Admixtures under the Equal Strength Grade

Fly ash (FA) and ground granulated blast-furnace slag (GGBS) are the most widely used mineral admixtures in engineering. However, their roles in concrete under the equal strength grade, a common comparison method in engineering, were seldom reported. This study investigated the chloride ion permeability and drying shrinkage of concrete samples containing FA or GGBS under an equal strength grade. The samples’ strengths and slumps maintained the same levels by adjusting the water-to-binder ratios and superplasticizer dosages. The results show that both FA and GGBS can promote the resistance to chloride ion penetration and decrease the chloride diffusion coefficients, especially at late ages, due to the hydraulicity of GGBS and pozzolanic activity of FA. Compared with FA, GGBS presents a greater reduction in the concrete permeability due to its higher reactivity. Forty percent replacement levels of FA and GGBS can decrease the penetration level from “high” of plain cement concrete to “moderate” and “low”, respectively. In addition, FA and GGBS can decrease the drying shrinkage of concrete at high replacement levels (30% and 40%). This decrease is more significant in the FA-containing concrete, with the shrinkage decreasing from approximately 400 με to 350 με at a 40% replacement level. The findings can provide scientific guidance for applying FA and GGBS in practical engineering.