Micro-filler Effect Research Articles

Photocatalytic NOx removal and self-cleaning performance of polymeric carbon nitride functionalized alkali-activated slag composites

Alkali-activated slag (AAS) materials have been extensively investigated and employed for the photocatalytic coating incorporation due to their favorable binding property and low carbon emissions. However, the effects of photocatalysts on the microstructure and mechanical performance of AAS composites remain controversial, which have a significant impact on the durability of the photocatalytic composites in the real-life service environment. Herein, polymeric carbon nitride (PCN), as a metal-free photocatalyst, was mixed with AAS materials to prepare photocatalytic composites for nitrogen oxide (NOx) removal and surface self-cleaning. The PCN dosage effects on hydration products, microstructure, as well as mechanical and photocatalytic performances of the photocatalytic AAS composites were systematically studied. The results show that while hydration product formations are hindered by the PCN addition, its presence contributes to the carbonization of AAS composites. Additionally, due to the PCN microfiller effect, the microstructure of AAS composites is improved with the PCN addition, and the compressive strength of AAS composites becomes stronger as PCN dosage increases from 0 % to 6 %. The photocatalytic NOx removal and self-cleaning performances of PCN-added AAS composites are firstly increased and then decreased with the PCN addition. These findings provide the theoretical basis and technical support for PCN-added AAS composites application which satisfies the requirement for a sustainable and low carbon footprint future.

Effect of limestone powder on properties of self-leveling mortar

Mixing limestone powder (LP) in the self-leveling mortar (SLM) can not only solve the problems of LP waste randomly piled up and secondary utilization of resources, but also reduce the raw material cost of SLM and have excellent mechanical properties. The effect of replacing fly ash (FA) with LP and replacing cement with LP after completely replacing FA on fluidity and strength of SLM are studied. The microstructure of SLM is measured by mercury intrusion porosimetry and scanning electron microscope. The results show that the initial fluidity and the 20-min fluidity of SLM decrease gradually with the increase of LP content. The strength of SLM increases and then decreases with the increase of LP replacing FA, and the strength is the highest when the addition of LP is 40%. When LP replaces cement after completely replacing FA, the strength of SLM decreases with the increase of displacement. Excessive LP can greatly damage the mechanical properties of SLM. The appropriate content of LP can improve the microstructure of SLM and promote the formation of hydration products, which is helpful to reduce the porosity and thus improves the structure density. This may be due to the chemical reaction and the microfiller effect of LP.

Photocatalytic Activity and Mechanical Properties of Cement Slurries Containing Titanium Dioxide

The effect of titanium dioxide (TiO2) on the mechanical properties of cement slurries including their benefits on air purification and abatement of pollutants is not well documented. Cementitious-based slurries are typically applied in thin layers as decorative coatings for existing facades, protection against an ingress of aggressive ions, or rainproof covers to minimize water penetration. Different parameters including the TiO2 concentration, dispersion time during batching, and applied thickness on top of existing mortar blocks are investigated in this paper. Tested properties included the flow, colorimetry, compressive/flexural strengths, bond to existing substrates, water absorption, and photocatalytic activity evaluated using an ISO 22197-1:2007 reactor. The results showed that the mechanical properties remarkably improved with TiO2 additions, up to 8% of the cement mass. This was attributed to two concomitant phenomena including a micro-filler effect that enhances the packing density and nucleation sites to promote strength development. The removal of nitrogen oxides from the atmosphere reached 92% when the TiO2 was added at a rate of 5% of the cement mass. Such data can be of particular interest to consultants and environmental activists searching for innovative materials capable of maintaining better ambient air quality in urban and modern cities.

Durability of Engineered Cementitious Composites Incorporating High-Volume Fly Ash and Limestone Powder

This study investigates the effects of using limestone powder (LSP) and high-volume fly ash (FA) as partial replacement for silica sand (SS) and portland cement (PC), respectively, on the durability properties of sustainable engineered cementitious composites (ECC). The mixture design of ECC included FA/PC ratio of 1.2, 2.2 and 3.2, while LSP was used at 0%, 50% and 100% of SS by mass for each FA/PC ratio. Freeze-thaw and rapid chloride ions penetrability (RCPT) tests were performed to assess the durability properties of ECC, while the compressive and flexural strength tests were carried out to appraise the mechanical properties. Moreover, mercury intrusion porosimetry (MIP) tests were performed to characterize the pore structure of ECC and to associate porosity with the relative dynamic modulus of elasticity, RCPT and mechanical strengths. It was found that using FA/PC ratio of more than 1.2 worsened both the mechanical and durability properties of ECC. Replacement of LSP for SS enhanced both mechanical strengths and durability characteristics of ECC, owing to refined pore size distribution caused by the microfiller effect. It can be further inferred from MIP test results that the total porosity had a vital effect on the resistance to freezing–thawing cycles and chloride ions penetration in sustainable ECC.

Volume stability and nano-scale characteristics of concrete composite containing natural zeolite

More environmentally friendly and sustainable cementitious component is essential for improving climate warming and protecting the environment. The effects of zeolite powder (ZP) are investigated in this study on the mechanical properties of concrete and their efficacy in improving the volume stability (dry shrinkage and creep) of the concrete with different specimen sizes. Nanoindentation and scanning electron microscopy are used to characterize the microstructure of concrete. The results show that although ZP reduces the 7-day compressive strength of concrete, the 28-day strength of concrete with 20% ZP is similar to that of the plain concrete. The use of ZP effectively improves the volume deformation of concrete, and concrete with 20% ZP has the lowest dry shrinkage and creep. Meanwhile, an appropriate amount of ZP (20%) can improve the compactness of the microstructure (matrix and interface transition zone) due to its microfiller effect, pozzolanic reactivity and internal curing effect. From the nano-microscale level analysis, ZP can increase the content of high-density calcium silicate hydrate (C–S–H) and reduce the content of low-density C–S–H in the cementitious composition, which is beneficial to the reduction of concrete creep.

Effect of pigments on bond strength between coloured concrete and steel reinforcement

The effect of pigments on mechanical properties of coloured concrete intended for structural applications, including the bond stress-slip behaviour to embedded steel bars, is not well understood. Series of concrete mixtures containing different types and oncentrations of iron oxide (red and grey colour), carbon black, and titanium dioxide (TiO2) pigments are investigated in this study. Regardless of the colour, mixtures incorporating increased pigment additions exhibited higher compressive and splitting tensile strengths. This was attributed to the micro-filler effect that enhances the packing density of the cementitious matrix and leads to a denser microstructure. Also, the bond to steel bars increased with the pigment additions, revealing their beneficial role for improving the development of bond stresses in reinforced concrete members. The highest increase in bond strength was recorded for mixtures containing TiO2, which was ascribed to formation of nucleus sites that promote hydration reactions and strengthen the interfacial concrete-steel transition zone. The experimental data were compared to design bond strengths proposed by ACI 318-19, European Code EC2, and CEB-FIP Model Code.

Interaction between composition and microstructure of cement paste and polymeric carbon nitride

As a metal-free and visible-light-responsive photocatalyst, polymeric carbon nitride (PCN) is an ideal alternative to traditional titanium dioxide employed in photocatalytic cementitious materials (PCM) for environmental remediation. However, the interaction between the composition and microstructure of cementitious materials and PCN is far from clear. Herein, the hydration behavior, phase composition, microstructure, compressive strength and nitrogen oxides removal of the PCN-modified paste with different dosage of PCN at varying curing ages were investigated and the key factors governing the photocatalytic activity of the PCM were studied. The results show that the porosity of the PCN-modified pastes presented an increasing trend compared to the reference, but the micro-filler effect of PCN contributed to the varying reductions in the volume of harmful pores, which are mainly responsible for the highest compressive strength of 0.5% PCN-added pastes at 3 days and 28 days. Although the kinds of hydration products were not affected with the addition of PCN, the carbonates could be regulated to the well-crystallized and flower flaky calcites in the presence of PCN at 28 days. The well-crystallized calcite would be regarded as potential acceptors of photo-induced holes to promote the separation of electron-hole pairs on the PCN. The promoting effect of electron transfer could outperform the negative effect of the decreased porosity caused by ongoing hydration and carbonization, resulting in an enhanced photocatalysis of PCM with the increase of curing ages. The findings from this study would provide a novel understanding on the improvement of photocatalytic efficiency for PCM against the shielding effects of hydrates and carbonates.

Machine learning-based compressive strength modelling of concrete incorporating waste marble powder

In recent years, the volume of waste marble powder (WMP) from ornamental stone factories has increased rapidly, causing environmental concerns of soil, water and air pollution. While some studies have explored the benefits of incorporating WMP in concrete mixtures, the lack of pertinent data and a comprehensive understanding of how WMP influences the engineering properties of concrete has hindered the large-scale applications of WMP in the concrete industry. Therefore, this study examines the capability of machine learning (ML) to model the compressive strength (CS) of concrete incorporating WMP since it is the most specified property of concrete. WMP can improve the performance of concrete mainly owing to a physical microfiller effect and providing preferential sites for the nucleation and growth of early-age cement hydration products. However, considering that the pozzolanic reactivity of WMP is insignificant as demonstrated by phase composition and thermogravimetric results, its incorporation rate in concrete mixtures should be limited to a specific dosage, which can be optimized using ML techniques. ML modelling results showed that the CS of WMP concrete could be predicted with high accuracy (R2 > 0.97) using extreme gradient boosting (XGB) and artificial neural networks (ANN) informational models, with ANN being more sensitive to the content of WMP. The feature importance results, with multicollinearity consideration, showed that the role of WMP in strength development could be mainly limited to 10–20% due to its inert nature.

Effects of dolomite powder on the properties of C30 and C50 concretes

This study focused on the effects of dolomite powder on the properties of C30 and C50 concretes. The microstructure, splitting tensile strength, compressive strength and fracture toughness property of concretes incorporating dolomite powder were measured by mercury intrusion porosimetry (MIP), pressure testing machine and universal testing machine. Higher splitting tensile strength, compressive strength and fracture toughness of concretes could be seen with the increase of dolomite powder dosage within 90 days. After 1 day of curing, splitting tensile strength, compressive strength and fracture toughness of C30 and C50 concretes could be improved considerably. The positive effects of dolomite powder on the splitting tensile strength, compressive strength and fracture toughness decreased with the increase of curing age. Because the nucleation effect, micro-filler effect and mix proportions design of dolomite powder were beneficial to the refinement of pore structure of concretes, and dolomite powder had less influence on the later stage of cement hydration. The splitting tensile strength equations expressed in terms of the compressive strength was proposed. The analysis of regression equation proved that the equation of relationship between compressive strength and splitting tensile strength of concretes containing dolomite powder in this study had high prediction accuracy.

Moisture dependence of electrical resistivity in under-percolated cement-based composites with multi-walled carbon nanotubes

Cement-based piezoresistive composites have attracted significant attention as smart construction materials for embedding self-sensing capability in concrete infrastructure. Although a number of studies have been conducted using multi-walled carbon nanotubes (MWCNTs) as a functional filler for self-sensing cement-based composites, studies addressing the influence of the internal moisture state on the electrical properties are relatively scant. In this study, we aim to experimentally investigate the effect of internal moisture state on the electrical resistivity of cement-based composites containing MWCNTs as an electrically conductive medium to raise a need for calibration of self-sensing data considering the internal moisture state. To this end, the moisture dependence of electrical resistivity in under-percolated cement-based composites was mainly evaluated, along with other material properties such as strength, shrinkage, and flowability. Results revealed that the electrical resistivity increased almost linearly as the internal relative humidity (IRH) decreased, and the increase was more pronounced below the percolation threshold. In addition, it was found that the strength gained by the microfiller effect of MWCNTs was significantly reduced particularly in under-percolated mixtures, leading to overall strength reductions. Furthermore, this study showed that the more the MWCNT was added, the smaller the flowability was obtained due to the increased viscosity of the mixture. The findings of this study are expected to provide pivotal information for accurate and reliable interpretations of self-sensing data generated by MWCNT-embedded cement-based composites.

Microfiller Influence on the Modified Cement Granulometric Composition

The aim of the work is to study the microfiller effect on the granulometric composition of the modified cement. A scanning electron microscope RМ-106 I was used for microscopic analysis. The survey was carried out in reflected electrons. The chemical analysis of the materials’ structure was investigated by energy dispersive spectroscopy (EDS). The distribution of particles of mineral components was evaluated with a Microsizer 201C laser particle analyzer with a range from 0.2 to 600 μm. Microscopic analysis of the samples of microsilica MK-85 shows that all particles are spherical with an average grain size of about 5 microns and consist of amorphous glass with a different set of particle fractions. The results of X-ray phase analysis of condensed microsilica grade MK-85 show that it consists mainly of silicon dioxide in an amorphous form. The introduction of mineral additives with a high specific surface in the composite Portland cements composition in an amount of more than 5% is not rational without the use of superplasticizers, since the water demand increases sharply, which reduces the cement stone strength. The introduction of a microfiller provides an increase in the compressive strength of a cement stone at the age of 28 days of normal hardening by an average of 37%.

Properties of cement mortar containing recycled glass and rice husk ash

Using recycled glass (RG) to replace river sand in the production of cement-based materials saves the increasingly depleting natural sand resources. Previous studies have shown that the smooth surface and reactive silica of RG adversely affected its bonding with the cement paste and thereby caused a potential alkali-silica-reaction (ASR). This study used rice husk ash (RHA) as an eco-friendly mineral admixture to ameliorate the properties of the RG incorporated mortar. A fixed replacement of 50% RG was used to replace sand, while varying proportions (10%, 20% and 30%) of RHA were adopted to replace cement. For comparison, a mixture containing only sand and cement was used as the reference sample. The flexural and compressive strength, water absorption, ASR expansion, and rapid chloride mitigation (RCM) of the hardened samples were evaluated. In addition, SEM, XRD, and TG analysis were employed to analyze the microstructures and chemical compositions of different samples. The results showed that incorporating RG as a river sand replacement in cement mortar reduced flexural and compressive strength and increased water absorption and chloride ion penetration. Moreover, the ASR expansion value (0.34%) was beyond the permissible limit (0.1) indicated by the ASTM C1260. The addition of RHA improved the mechanical properties and durability of the cement mortar at a later curing age as a result of the RHA-induced pozzolanic reaction and micro-filler effect. By converting portlandite (CH) derived from cement hydration into secondary C-S-H, the use of RHA greatly reduced the porosity (augmenting the compressive and flexural strength) and concurrently suppressed the RG-induced ASR expansion. The results of XRD, SEM and TG analysis corresponded well with the macro-property analysis and helped to elucidate the underlying mechanisms of the RHA-induced beneficial effects. Findings from this study provide new insights into the potential use of eco-friendly RHA in addressing the mechanical and durability problems associated with the use of RG as aggregate in cementitious materials.

EFFECTS OF METAKAOLIN ON COMPRESSIVE STRENGTH AND PERMEABILITY PROPERTIES OF PERVIOUS CEMENT CONCRETE

This paper presents the experimental results on the effect of metakaolin (MK) as a replacement of cement in pervious cement concrete based on compressive strength, void ratio and permeability test. Metakaolin was used to replace Portland Cement Composite (PCC) in pervious concrete by 10% (by wt.). The results show that pervious concrete sample containing 10% metakaolin with 1% superplasticizer exhibited 4 times higher compressive strength at 7 days when compared to normal cement concrete. In addition, the continuous voids of 10%MK concrete sample was found higher than PCC only, indicating the effectiveness of metakaolin in improving the interfacial bond of the binders due to micro-filler effect of metakaolin and the additional CSH gel formation. The continuous voids of pervious concrete with 10% MK is 17%, which is higher than the percentage of continuous voids in normal pervious concrete. This finding is also supported by the infiltration rate of concrete samples. Furthermore, the microstructure analysis through Backscattered Electron Imaging and X-Ray Diffraction reported denser matrix and CH reduction in polished paste samples due to 10%MK addition.

Ultrasonic evaluation of strength properties of cemented paste backfill: Effects of mineral admixture and curing temperature

This paper presents the findings of a research study designed and conducted to investigate the effects of mineral admixture and curing temperature on uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) behavior of laboratory-prepared cemented paste backfill (CPB) samples. A total of 290 CPB samples were prepared at different replacement rates (10–80%), cured at various temperatures (10–50 °C), and respectively subjected to both UPV and UCS testing after curing times of 3, 7, 14, 28, 56 and 90 days. The obtained experimental results show that the addition of fly ash (FA) can lead to an increase or decrease trend in UCS and UPV behavior of CPB samples, depending on the replacement level of admixtures. There is a competition between the strength-increasing factor (micro-filler effect of FA) and strength-decreasing factor (lower amount of cement hydration products induced by replacement ratio). Both UPV and UCS are found to decrease with increasing blast furnace slag (Slag) replacement level mainly attributable to its low pozzolanic reactivity. Besides, the curing temperature has a significant influence on UCS and UPV behavior, depending on the curing time. Results also suggest that UPV is less sensitive to the variation in the admixture dosage and curing temperature than UCS. As a result, there exists a clear linear relationship between UPV and UCS behavior of both CPB samples prepared with FA and/or Slag admixtures, and CPB samples tested at each curing temperature. The main findings of this research study suggest that the UPV test can be reliably used for predicting CPB’s strength properties, saving money and time to mine operators.

An experimental study on compressive behaviour of cemented rockfill

• Technical information and data for better optimization and design of cemented rockfill (CRF) are presented. • Strength and stress-strain behaviour of CRF are a function of the packing density of the aggregates. • CRF with coarser particles and the best grain size distribution has the highest strength. • Addition of sand can increase the strength of CRF. • A partial replacement of ordinary Portland cement with fly ash improves the strength of the CRF. Cemented rockfill (CRF) has more superior mechanical properties (e.g., compressive strength, stiffness, cohesion and friction angle) over other types of backfill material, such as cemented paste backfill (CPB) and hydraulic fill, with the same amount of binder. A comprehensive understanding of the mechanical performance of CRF is critical for effectively applying CRF technology to underground mines. In this paper, the effects of aggregate gradation, the addition of sand, and binder content and type on the uniaxial compressive strength (UCS) and stress-strain behaviour of CRF are experimentally investigated for up to 90 days of curing. The results show that CRF with coarser particles and the best grain size distribution has the highest strength over that with uniform-sized rock aggregate, and the strength of the CRF increases with increased maximum particle size of the rock aggregate. The strength of the CRF increases in proportion with the amount of ordinary Portland cement (OPC). The addition of sand enhances the strength of the CRF samples; the extent of the increase in strength depends on the sand/aggregate replacement ratio. A partial replacement (20–50%) of OPC with fly ash (FA) appears to improve the strength of the CRF samples due to the micro-filler effect, whereas a negative effect is observed when blast furnace slag (Slag) with relatively low strength activity index is used instead. Moreover, the stress-strain response of CRF is strongly influenced by the curing age, aggregate gradation, addition of sand, and binder content and type. The results of this investigation provide technical information for designing cost-effective, safe and durable CRF structures in underground mines.

Graphene oxide modified Strain Hardening Cementitious Composites with enhanced mechanical and thermal properties by incorporating ultra-fine phase change materials

A novel Strain Hardening Cementitious Composite (SHCC) was developed by incorporating ultra-fine (30 μm) phase change materials (PCMs) composites and Graphene Oxide (GO) to enhance its mechanical and thermal performance. The ultra-fine PCMs composites were fabricated by intruding 75.0 wt % of paraffin (PA) into 25.0% of expanded perlite (EP) using the vacuum impregnation method. The ultra-fine PCMs can be used as ultra-fine aggregates to improve the composites’ thermal properties without compromising the compressive strength, due to the micro-filler effect and pozzolanic properties of the PCMs composites. GO was introduced to further improve the tensile and flexural performance and the mechanisms involved are comprehensively discussed. Regarding thermal properties, the addition of ultra-fine PCMs composites not only reduced the thermal conductivity by 56.6% but also improved the specific heat capacity and thermal insulation properties of the SHCC, which enabled the structural concrete members with the integration of load-bearing and indoor temperature control. In conclusion, a novel SHCC with enhanced thermal and mechanical properties by adding ultra-fine PCMs composites and GO shows a great potential for green buildings with the integration of structure, energy conservation and durability.

Creep behavior of concrete containing glass powder

Glass powder (GP) is a solid waste with increasing reserves. GP can be used as a supplementary cementitious material (SCM) to produce concrete in order to effectively save resources and solve environmental pollution problems. The effect of GP to replace cement partially by weight on the compressive strength, elastic modulus and creep of concrete has experimentally been studied, and the internal microstructure is also determined by mercury intrusion porosimetry, scanning electron microscope and nanoindentation techniques. The results show that the use of GP reduces the compressive strengths and elastic modulus at the early ages, but the use of GP content less than 20% increases the compressive strengths and elastic modulus at the later ages. The use of GP content less than 20% can obviously reduce the creep and the use of 20% GP content seems to be the best in terms of the reduction of the creep. The use of GP with the appropriate content can effectively improve the internal microstructure of concrete and increase the content of high density calcium silicate hydrate at the later ages which is helpful in reducing the creep. This may be attributed to the pozzolanic reaction and microfiller effect of GP.

Biochar as a carbon sequestering construction material in cementitious mortar

Recent efforts to attain carbon negative construction practices in Singapore and other developed countries leads to a search for construction materials that can reduce net carbon emission associated with concrete constructions. One such material is biochar which can sequester fixed carbon in its structure. Therefore, using biochar as a mixed-in component in cementitious material can reduce the net greenhouse emission associated with concrete constructions. Our study focuses on application of biochar derived from mixed-wood saw dust as a cement replacement in mortar. Experimental findings suggest that, due to its fine particle size and microfiller effect, up to 4% cement replacement by biochar yielded slight improvement in compressive strength while reducing sorptivity by about 70% after 28 days. Improvement in strength and permeability of mortar by incorporating biochar suggest that it can be successfully deployed as a carbon sequestering concrete construction material. Durable and strong infrastructure means reduced vulnerability to damage and thus need for subsequent repairs over its service lifespan. This will help contribute toward economic and environmental sustainability of buildings.

Filler effect of pozzolanic materials on the strength and microstructure development of mortar

The utilization of pozzolans in cementitious system (concrete and mortar) minimizes both cost and energy. It also enhances mechanical strength and durability of the system. The total contribution of pozzolans can be categorized into two: (i) physical or filler effect which is attributed by the fineness of the particles and (ii) chemical or pozzolanic effect which is attributed by the pozzolanic reaction. It is difficult to quantify the strength development of cementitious system caused by the filler and pozzolanic effect separately. Therefore, the individual contribution of pozzolans in cementitious system because of its physical and chemical effects need to be profoundly understood by the scientific community. This paper reviews available literatures to understand the effect of non-reactive fillers that attributed as the microfiller effect of pozzolans in cementitious systems. The previous studies utilized chemically inactive materials that attributed only the microfiller activity of pozzolans for a partial replacement of cement. It was reported that filler effect is equal or sometimes more significant than pozzolanic effect in concrete. A larger range of replacement percentages (like 5%, 10%, 15% or 10%, 20%, 30% etc.) was used in the previous studies. However, probabilities of the optimum compressive strength because of the filler effect may lie in between two larger range of replacement percentages. Therefore, an experimental work is also carried out using natural ground sand of size 7.6-μm at a lower range of cement replacement percentages (like 2.5%, 5%, 7.5% etc.) in mortar. Compressive strength of mortar at different ages and microstructure analysis of mortar at 28 days were performed in this study. Test results showed that the filler effect is more pronounced at a lower replacement percentages of cement (0-10%) while using smaller non-reactive fillers. The maximum strength due to filler effect of ground sand is acheieved at 7.5% replacement of cement. Scanning Electron Microscope (SEM) images also confirmed the effect of fillers on the microstructure development of mortar.

Micro Filler Effects of Silica-Fume on the Setting and Hardened Properties of Concrete

The use of supplementary cementitious material is gaining much attention owing to its high pozzolanic property and further improvement in strength properties. Silica-fume is one among the widely used pozzolanic material which exhibits high cementing efficiency due to high silica content. This study presents comprehends a detailed insight on the hydration properties of silica fume with cement. Silica fume consists of very fine particle size and contains silica content more than 90%. The cement hydration results in the formation of calcium hydroxide and this is consumed with the addition of silica fume and results in additional calcium silicate hydrate. This compound primarily envisages the strength and improved microstructure of concrete. Addition of silica-fume fills in the spaces between cement grains. The test results showed that higher compressive strength of concrete is obtained by using 8.0% of silica-fume at 7 and 28 days was 48.25 and 55.83 MPa, respectively. This phenomenon is frequently referred to as particle packing or micro-filling. Even if silica fume did not react chemically, the micro-filler effect would lead to significant improvements in the microstructure of concrete. A comprehensive review has been carried out in this study to give a good understanding on the advantages of pozzolanic properties of silica fume in cement concrete.