Blended Cementitious Materials Research Articles

Coupled rheo-physical effects of blended cementitious materials on wet packing and flow properties of inert suspensions

In addition to particle-liquid interaction, the flowability of blended-cementitious suspensions depends on the physical properties and packing of solid particles. The coupled physical effects of various single and blended cementitious materials on the flow behavior of inert suspensions was evaluated. General use cement (GU), ground-glass pozzolan, fly ash-F, blast furnace slag, limestone fillers, and their binary and ternary combinations were investigated. The blending effect on the wet packing and flowability of the investigated systems was highlighted. The overall dry flowability of the single powders and blended systems depends on the angles of repose (αF) and spatula (αS), which reflect their specific surface area. The dry physical parameters were in good agreement with their performance in suspension. The decrease of angles of repose and spatula resulted in higher maximum wet packing. All the investigated single powders showed higher relative alcohol demand and lower wet density than GU cement. The dry packing, morphology, and cohesion of blended cementitious materials influenced the minimum and relative liquid demand. Particles with higher aspect ratio and lower circularity increased the alcohol demand to initiate the flow of suspensions. Powders with higher angle values exhibited lower flowability. Good correlations were established to evaluate the coupled effects of different physical characteristics of powders on the wet packing of suspensions. Higher wet packing of single and blended systems having coarser average diameter values can be achieved by simultaneously reducing their compressibility and average diameter-to-fineness (d502/SSA) ratio values.

Global quantitative monitoring of the ion exchange balance in a chloride migration test on cementitious materials with mineral additions

The concrete pore solution changes during chloride transfer due to the species leaching and the dissolution/precipitation of compounds. The latter could affect the material porosity and the chloride diffusion coefficient. In order to quantify these changes, the global movement of species was monitored on blended cement materials during a chloride migration test. Compartment solutions and sample pore solutions were analyzed in order to quantify the ion exchange balance. Two migration test protocols were carried out using (i) NaOH, KOH and NaCl, and (ii) synthetic seawater and synthetic pore solution. The use of slag reduces the free chloride in the porosity by about 9 times. For the Portland cement material, a precipitation of 0.3%wt of Na, 0.6%wt of K and 1%wt of Cl participated in a porosity clogging of 60%. Finally, the materials with mineral additions reduce the portlandite dissolution during chloride transfer and the calcium leaching phenomena up to 26%.

Performance of rebar embedded in blended cement materials concrete under marine environmental conditions

A concrete structure mainly depends upon the protective action provided by the cover concrete. Corrosion of rebars due to chlorides and deterioration of concrete are mainly responsible for the reduction of service life of concrete particularly in marine environment. The service life ends when the protective action provided by the cover concrete is lost. The prediction of service life would be very useful to arrive at a cost effective strategy to be adopted regarding inspection, repairing, strengthening and replacement of corrosion affected concrete structures at appropriate time to prevent premature failure. This would be further useful in estimating the structural capacity to withstand the extreme aggressive conditions during the remaining service life of the concrete structures.

Scientific and technical studies on eco-efficient binary cements produced with thermally activated ichu grass: Behaviour and properties

The present research study analyses, for the first time, the viability of using thermally activated ichu grass as a supplementary cementitious material for the design of future eco-cements. To this end, the ichu ash resulting from the activation was characterised and its pozzolanic activity, the evolution of its mineralogical phases during the pozzolanic reaction and the physical-mechanical behaviour of the blended cementitious matrices were analysed. The results show that ichu ash exhibited high pozzolanic activity in a pure pozzolan/lime system as a consequence of its high reactive silica content. Conversely, its use in a pozzolan/cement system gave rise to negative effects due to the presence of important alkali contents in the ash (9.6% Na2O eq). The blended cements presented greater water demand, reduced capillary absorption, increased resistivity and lower mechanical properties (10–14%) as well as reduced average pore size than the reference mortar. These blended cement matrices comply with the physical-mechanical requirements established in the standards for the production of eco-cements.

Modelling of 3D microstructure and effective diffusivity of fly ash blended cement paste

Accurate prediction of microstructural evolution and ionic diffusivity in fly ash blended cement paste is significant for practical application and durability design of blended cementitious materials. This paper presents an integrated modelling framework for simulating 3D microstructure and effective ionic diffusivity of blended cement paste with various fly ash replacement levels and water-to-binder (w/b) ratios. A voxel-based hydration model using cellular automaton-like evolution rules was developed to simulate 3D microstructural development of fly ash blended cement, based on which the effective diffusivity was simulated using a lattice Boltzmann (LB) model for diffusion considering the contributions of both capillary pores and gel pores in C–S–H gels to ionic diffusion. A series of experiments were conducted to characterise the morphology of Portland cement and fly ash, hydration process and pore structure of fly ash blended cement paste and measure the effective ionic diffusivity. The simulation results agree well with experimental data in terms of hydration heat, calcium hydroxide content, degree of hydration of fly ash, porosity, and effective diffusivity, which suggests that the developed microstructure-based LB model for diffusion can predict the ionic diffusivity of fly ash blended cement paste with high accuracy. The addition of fly ash can help reduce the ionic diffusivity of cement paste particularly after the capillary porosity depercolation occurs due to the more tortuous diffusion paths in the pozzolanic C–S–H gels.

Visco-elastic behavior of blended cement pastes at early ages

This study aims at elucidating the visco-elastic behavior of hardening blended cement pastes, focusing on uniaxial basic compressive creep tests at early loading ages. Cement pastes with Portland cement only or blended with quartz or fly ash (both at a substitution level of 49% by volume of the total solids) were subjected to different loading scenarios.The results show that both blended systems had higher creep than pure cement paste at early ages and that the creep compliance of the blended system with fly ash was higher than with quartz. While this difference is in part due to the restraining effect of the elastic phases, the amount of C–S–H and the porosity, dissolution creep may also play a role. A numerical algorithm with generalized Kelvin-Voigt chain model was developed and it was capable of predicting with good accuracy the strain evolution of the blended cementitious materials at early ages.

Effect of mineral additions on the microstructure and properties of blended cement matrices for fibre-cement applications

This detailed study of the effect of three mineral additions (limestone, rice husk ash and activated coal mining waste) differing in composition and properties explored the behaviour of blended cements with a 25% replacement ratio. The aim was to select the optimal addition for improving the performance of natural fibre-reinforced cements. The pozzolanic, physical and mechanical properties as well as the pore structure of the blended cement matrices were examined. The findings showed that although rice husk ash is characterised by high pozzolanicity, it had a less favourable effect on the cement than expected, yielding porous, poorly compacted and hence weak matrices. The activated coal mining waste showed better performance, reaching similar strength to control mortar, better pore size refinement and an important reduction in mean pore size of 60% compared to control mortar after 60 days of curing. In light of those findings, this aluminosilicate addition is proposed as the most apt of the three studied for improving the quality of fibre-reinforced cements, keeping in mind that the interaction effect amongst the three mineral additions was not considered in the present work.

3D pore structure and mass transport properties of blended cementitious materials

The effect of supplementary cementitious materials on three-dimensional pore structure and how this influences mass transport properties are not well understood. This paper examines the effect of silica fume, fly ash and ground granulated blastfurnace slag on 3D structure of capillary pores (>0.24 μm) within 1003 μm3 cement paste for the first time using laser scanning confocal microscopy, combined with backscattered electron imaging and mercury intrusion porosimetry. Pastes containing different binder types, w/b ratios and curing ages were tested. Results show that SF enhances 3D pore structure from early ages whereas PFA and GGBS show improvements at later ages. SCMs not only reduce the volume and size of accessible pores, but also decrease connectivity and increase tortuosity, pore coordination number and formation factor. Measured 3D pore parameters were used as modelling inputs to estimate diffusivity and permeability. Predictions to within a factor of five from measured values were obtained.

Effect of a high content in activated carbon waste on low clinker cement microstructure and properties

In the context of cement industry sustainability and socio-economic development, one of the primary objectives of the circular economy is the use of industrial waste as a supplementary cementitious material in the manufacture of future eco-efficient binders. This paper reports a first-time study of the effect of large proportions of the activated carbon (AC) waste used in low clinker cements on the properties and structure of the new binders. The behaviour of blended cement matrices prepared with 20%–50% AC as a pozzolan was analysed in terms of their chemical, mechanical and physical (rheology, heat of hydration, drying shrinkage, microporosity) properties. Macroporosity was also assessed with computed tomography (CT). The findings showed that these blended cements meet standard chemical and rheological requirements and that the 50% AC binder qualifies as a low heat cement. Drying shrinkage was observed to intensify with higher percentages of AC. A rise in total porosity was attendant upon pore size refinement, with an increase in the <100 nm fraction. Compressive strength declined with rising replacement ratios. Further to the CT findings, macroporosity (0.001–0.09 mm3) also increased with AC content, especially in the binders bearing 50% of the addition.

Improvement of early-age properties for glass-cement mortar by adding nanosilica

Poor early-age performance (e.g. lower early strength, longer setting time) is an important technical challenge for the application of blended cementitious materials containing low reactivity or high volumes of supplementary cementing materials. In this study, the mechanism of using nanosilica (NS) to improve the early-age properties for cement mortars blended with glass powder (GP) and glass aggregates has been investigated. The results indicate that the addition of NS into glass-based cement mortar largely improved the early stiffening which was dependent on high specify surface area of the NS rather than cement hydration. Combining the use of NS and GP was conducive to compensate the delayed setting times and the strength losses caused by the incorporation of GP. These beneficial behaviors were associated with the physical, acceleration, pozzolanic and pore refinement effects of NS. In terms of heat of hydration, the inclusion of NS intensified and accelerated the appearance of the third exothermic peak (AFt to AFm) due to the absorption of sulfate ions by the increased C-S-H formation. Also, the total hydration heat liberated was found to correlate linearly with the corresponding early-age compressive strength. Microstructural analysis suggest that NS significantly helped to densify the microstructure of the GP blended cement matrix and improved the interface between the GP particle and the binder matrix. This was verified by the contribution of NS on refining the coarse pore size caused by the use of GP as a replacement of cement.

Mechanical properties of recycled aggregate concrete containing ternary blended cementitious materials

Abstract This paper presents the effect of silica fume (SF) on early-age and long-term mechanical properties of recycled aggregate concrete containing slag. In this study six series of mixes are considered. The first series is control concrete containing 100% ordinary Portland cement (OPC) and 100% natural aggregates. The second series is similar to the first series in every aspect except the natural coarse aggregate (NCA) which was partially replaced by 50% (by wt.) recycled coarse aggregate (RCA). The third series is also similar to the second series except the OPC which is partially replaced by 50% slag. The effects of 5, 10 and 15% (by wt.) SF on mechanical properties of concrete is evaluated in fourth, fifth and sixth series, respectively. Compressive strength, indirect tensile strength and modulus of elasticity of above concretes are measured at 3, 7, 28, 56 and 91 days. Results show that the addition of 50% slag significantly reduced the above mechanical properties of concrete containing 50% RCA at early age. Among three SF contents, the 10% SF improved the above mechanical properties of recycled aggregate concrete containing slag at early ages (3 and 7 days) as well as at 28 days. The addition of 10% SF also improved the 56 and 91 days compressive and tensile strengths of recycled aggregate concrete containing slag. It is also found that the long-term (56 and 91 days) compressive and tensile strengths of recycled aggregate concrete containing slag and 10% SF are even higher than the OPC concrete containing 50% RCA and control concrete, respectively. It is also observed that the slow pozzolanic reaction of slag contributed to the long-term compressive and tensile strengths of recycled aggregate concrete containing slag and 10% SF. Strong correlations of measured compressive strength with indirect tensile strength and elastic modulus of above environmentally friendly concretes are also established.

Estimating the mechanical properties of hydrating blended cementitious materials: An investigation based on micromechanics

The hydration model of Parrot & Killoh (1984) has been extended to blended cements and coupled to a micromechanical scheme similar to that of Pichler & Hellmich (2011) to estimate the Young modulus and the compressive strength of cementitious materials as a function of time. A finite aspect ratio of 7 is introduced to describe the shape of the hydrates and improve the estimate of the early age strength by the micromechanical scheme. Furthermore, accounting for the stress fluctuations in the cement paste partly explains the fact that the compressive strength of a concrete can be lower than that of its cement paste. Finally, the estimated physical properties are compared to numerous experimental measurements from the literature and new experimental measurements on blended cement pastes featuring significant weight fractions of limestone filler, fly ash or silica fume. It is shown that the present model slightly overestimates the dilution effect.

The Development of a Low Carbon Cementitious Material Produced from Cement, Ground Granulated Blast Furnace Slag and High Calcium Fly Ash

This research represents experimental work for investigation of the influence of utilising Ground Granulated Blast Furnace Slag (GGBS) and High Calcium Fly Ash (HCFA) as a partial replacement for Ordinary Portland Cement (OPC) and produce a low carbon cementitious material with comparable compressive strength to OPC. Firstly, GGBS was used as a partial replacement to OPC to produce a binary blended cementitious material (BBCM); the replacements were 0, 10, 15, 20, 25, 30, 35, 40, 45 and 50% by the dry mass of OPC. The optimum BBCM was mixed with HCFA to produce a ternary blended cementitious material (TBCM). The replacements were 0, 10, 15, 20, 25, 30, 35, 40, 45 and 50% by the dry mass of BBCM. The compressive strength at ages of 7 and 28 days was utilised for assessing the performance of the test specimens in comparison to the reference mixture using 100% OPC as a binder. The results showed that the optimum BBCM was the mix produced from 25% GGBS and 75% OPC with compressive strength of 32.2 MPa at the age of 28 days. In addition, the results of the TBCM have shown that the addition of 10, 15, 20 and 25% of HCFA to the optimum BBCM improved the compressive strength by 22.7, 11.3, 5.2 and 2.1% respectively at 28 days. However, the replacement of optimum BBCM with more than 25% HCFA have showed a gradual drop in the compressive strength in comparison to the control mix. TBCM with 25% HCFA was considered to be the optimum as it showed better compressive strength than the control mix and at the same time reduced the amount of cement to 56%. Reducing the cement content to 56% will contribute to decrease the cost of construction materials, provide better compressive strength and also reduce the CO2 emissions into the atmosphere.

Non-destructive tracing on hydration feature of slag blended cement with electrochemical method

This paper aims to use electrochemical impedance spectroscopy (EIS) with a novel equivalent circuit (EC) model to examine the hydration behavior of cement materials that incorporate ground granulated blast furnace slag. The experimental results suggest that the electrochemical impedance behavior of blended cement materials vary depending on the slag content. Also, the resistance associated with the ion transport process increases gradually along with the hydration process, and decreases as the slag is incorporated into the cement. In addition, we describe the linear relationship between the Rct1 value and the compressive strength for different slag contents and curing ages. The proposed method of EIS for slag blended cement materials, and the reliability of the new equivalent circuit model, is investigated across the entire hydration process of slag blended cement materials. Finally, the correlation of the compressive strength and the Rct1 value of blended cement materials with different slag contents are analyzed.

Characterization of carbonation behavior of fly ash blended cement materials by the electrochemical impedance spectroscopy method

The carbonation behavior of fly ash blended cement materials is studied by the electrochemical impedance spectroscopy (EIS) method, and a novel equivalent circuit model Rs(Q1(Rct1W1)) (Q2(Rct2W2)) is proposed to investigate the influence of fly ash on the carbonation process in the cementitious materials. The experimental results demonstrate that the diameter of the impedance arc in high frequency region increases as carbonation progresses. Increasing the amount of fly ash incorporated in the cement paste is also found to enlarge the high frequency arc. The carbonation process can be quantified by the parameter Rct2 extracted from the equivalent circuit model Rs(Q1(Rct1W1)) (Q2(Rct2W2)). It is found that the Rct2 value increases with increase in fly ash content. A linear relationship between the Rct2 value and the carbonation time is also observed. As a consequence, prediction of the carbonation depth of fly ash bended cement materials can be achieved through knowledge of the Rct2 value.

Physical–mechanical behavior of binary cements blended with thermally activated coal mining waste

This research work deals with the technical viability of manufacturing new eco-efficient cement blended with thermally activated coal mining waste (ACMW). The physical–mechanical results obtained in the present work showed that the addition of ACMW (up to 20% of replacement) modified the physical and mechanical properties of the blended cement matrices. The blended cements required a great water demand, slightly accelerated settings times and revealed gain in compressive strengths at early curing times. In general terms, blended cements containing up to 20% ACMW meet the chemical, physical and mechanical requirements set out by the EN 197-1 European standard.

Durability of Blended Cement Pastes Containing Ceramic Waste as a Pozzolanic Addition

Durability is one of the focal points of recent research on the behavior of new blended cement matrices in aggressive environments. The material selected for this study was ceramic waste (CW) rejected by Spanish manufacturers, primarily for reasons such as unsuitable kiln temperature or dimensional or mechanical failure. The resistance of CW‐containing cement pastes to three aggressive environments (SO42−, Cl−, and substitute seawater) was tested using the Koch–Steinegger method in this in‐depth analysis of the effect of CW on the chemical resistance of new blended matrices. The samples were also tested for performance in freeze–thaw cycles. The reaction mechanism was analyzed using X‐ray diffraction (XRD), pore‐size distribution, scanning electron microscopy (SEM), and backscattered electron images (BSE) with energy‐dispersive X‐ray (EDX) techniques. The results showed that CW contributed to cement resistance to such media; this enhancement of its mechanical properties was the result of the pozzolanic reaction induced by the addition of CW.

Scientific and technical aspects of blended cement matrices containing activated slate wastes

The extraction of slate for use as a construction material generates large quantities of waste (between 75% and 90% in weight), which are dumped on landfill sites, with the ensuing technical, economic, environmental, and social problems. One possible way of reusing this raw waste is through its thermal activation to produce a new cementitious material for the manufacture of eco-efficient cements.An assessment is presented in this study of the chemical, mineralogical and pozzolanic properties of ash waste, activated at 1000°C over 2h, as well as a study of the main technical properties of blended cements prepared with 10% and 20% slate ash. The results show the high pozzolanic activity of the slate ash, principally over the seven first days, forming CSH gels as a principal hydrated phase of the pozzolanic reaction, followed by randomly interstratified chlorite/smectite phases and monosulfoaluminate [C3A·SO4Ca·12H2O]. These blended cements prepared with 10% and 20% activated slate waste comply with both the physical and the mechanical requirements of current European standards.

Influence of activated drinking-water treatment waste on binary cement-based composite behavior: Characterization and properties

Drinking water treatment plants regularly dispose of large volumes of industrial sludge in landfill sites, which often has negative environmental consequences. The calcination products of these kaolinite-based sludges have properties that could make them appropriate supplementary cementing materials in the production of blended binary cements.This research analyses the pozzolanic and thermodynamic properties of a Venezuelan drinking water sludge activated at 600°C for 2h and its behavior in blended cement matrices prepared with 15% Activated Waste (AW) and 85% Ordinary Portland Cement (OPC). Our results show that this activated drinking water sludge presents high pozzolanic properties, mainly during the first 24h of reaction. The XRD, SEM/EDX and thermodynamic studies confirm the formation of C2ASH8, C–S–H gels and C4AH13 as the hydration products from the pozzolanic reaction. The binary mixture of 15% AW/85% OPC complied with the physical and mechanical specifications contained in current European cement standards.

Strength development of optimised cementitious materials containing fly ashes and silica fume

The objective of this study was to formulate a new cement replacement material using fly ashes. The strength development characteristics of two types of new ternary blended cementitious materials produced from three different types of fly ashes and silica fume (SF) were investigated in this study. The influence of water content, alkali activation synthesis by water dispersing agent on the ternary blends was revealed. The optimised blended mortar containing two different types of fly ashes synthesised with SF was reported to show more compressive strength than the control cement mortar when dispersed with polycarboxylate-based superplasticiser rather than sodium hydroxide (NaOH) activation.