Additional Calcium Silicate Hydrate Research Articles

Improvement of strength and microstructure of low-carbon cementitious materials with high volume of calcined coal gangue

The accumulation of coal gangue poses significant environmental challenges due to its massive volume and low reactivity. This study investigates the influence of calcium hydroxide (Ca(OH)₂) and gypsum on the mechanical properties, hydration, and pore structure of low-carbon cementitious materials incorporating high volumes of calcined coal gangue (CCG) and limestone. The results showed that the addition of Ca(OH)₂ significantly increased compressive strength, with a 19 % improvement at 28 days in LCC-40-P mix, which contained 40 % cement and 2.73 % Ca(OH)₂ by weight. The incorporation of 10 % gypsum in the LCC-40-P mix and 20 % gypsum in the LCC-70 mix (containing 70 % cement without Ca(OH)₂) effectively refined the pore structure, reduced overall porosity, and enhanced the material's density and mechanical properties, resulting in compressive strengths of 38.4 MPa (72 % of the strength of Portland cement) and 50.2 MPa (94 % of the strength of Portland cement) at 28 days, respectively. Microstructure and hydration heat tests showed that the addition of Ca(OH)₂ accelerates the hydration reaction and significantly enhanced compressive strength by ensuring sufficient Ca(OH)₂ for pozzolanic reactions, leading to the formation of additional calcium silicate hydrate, calcium aluminate silicate hydrate and carboaluminate phases. Gypsum refined the pore structure by shifting the pore size distribution towards smaller sizes, reducing overall porosity, and increasing the proportion of gel and small capillary pores. These findings highlight the potential of using CCG with optimized additives to develop sustainable, low-carbon construction materials with enhanced performance characteristics.

Understanding the role of natural pozzolana in regulating the early hydration reaction process and microstructure of Portland cement

The present study examines the regulatory role of natural pozzolana (NP) on the early-age hydration process and microstructural development of Portland cement. Through a series of experiments, including low-field nuclear magnetic resonance (NMR), X-ray diffraction (XRD), thermogravimetric (TG) analysis and scanning electron microscopy (SEM), it was found that NP significantly influences the hydration kinetics and chemical shrinkage of cement paste. The addition of NP was shown to reduce the early-age chemical shrinkage and refine the microstructure by decreasing the quantity of harmful pores and increasing harmless pores, as evidenced by the bimodal distribution observed in pore size distribution (PSD) analysis. XRD and TG results indicate that NP reacts with calcium hydroxide to form additional calcium silicate hydrate (C-S-H) gel, thus improving the interfacial transition zone and resistance to carbonation. SEM micrographs further confirm the improved microstructure with fewer microcracks. The findings suggest that NP can be effectively utilized to optimize the early-age performance of concrete, offering a sustainable approach to improving its durability and long-term structural integrity.

Synergistic effect of nano silica and metakaolin on mechanical and microstructural properties of concrete: An approach of response surface methodology

Nano and micro materials are both effective individually in enhancing the mechanical and microstructural properties of concrete. The combination illustrates an iconic shift in material engineering to produce concrete with distinctive characteristics. In this work, the combined effect of Nano Silica (NS) and Metakaolin (MK) on the mechanical and microstructure properties were examined by conducting compressive strength, split tensile strength, and Field Emission Scanning Election Microscope (FE-SEM) with Energy-dispersive X-ray (EDX) analysis, X-ray Diffraction (XRD) spectroscopy, Fourier Transform Infra-Red (FTIR) spectroscopy, respectively. The concrete matrix was investigated by varying the concentration of NS and MK with different Water-Binder Ratio (WBR). Further, the Response Surface Methodology (RSM) technique was used to identify the complex interaction between NS (1–3 %) and MK (5–20 %) at different WBR (0.35, 0.40 and 0.45). The synergistic effect between NS and MK resulted in enhanced compressive and split tensile strengths of the concrete. The optimum mix proportion of the concrete was found to be 2 % NS and 12.5 % MK at a WBR of 0.4. The compressive strength enhancements for the optimum mix proportion were 35.75 %, 34.4 %, 33.1 %, and 32.5 %, while the split tensile strength enhancements were 26.56 %, 25.92 %, 20.95 %, and 17.8 %, respectively on the 7th, 28th, 56th, and 90th day. The RSM technique developed for all the mixes has been statistically validated to have less than 5 % of mean error. Moreover, the microstructural analysis revealed early hydration, formation of additional Calcium Silicate Hydrate (C-S-H) products, and presence of dense microstructure resulting in improved microstructural properties. The incorporation of NS and MK in the concrete changes the concrete’s configuration at the nano and micro levels, thus paving the way for the development of novel and sustainable construction materials.

Influence of multi-stage processing and mechano-chemical treatments on the hydration and microstructure properties of recycled aggregate concrete

On account of the shortage of naturally occurring coarse aggregate, recycled aggregate (RA) made from crushed concrete debris is now used in the construction industry. With this rise in the utilisation of recycled aggregate in the construction sector, there has been extensive research into ways to improve its quality. The significant fraction of mortar remains that are left on the RA surface is the primary factor that affects its quality. Concrete made from RA loses strength and mechanical performance due to the attached mortar's increased porosity and water absorption values and the frailer transition region between the new mortar and aggregates. In order to minimise the old cement fractions and increase the quality, this paper studies the effect of concrete incorporating multi-stage processed RA from demolished concrete waste, followed by treatment with mechanical abrasion and sodium silicate immersion. The recycled aggregates were produced through multi-stage jaw crushing, followed by utilising natural aggregate, recycled aggregate, and recycled aggregate obtained after mechanical abrasion, followed by sodium silicate treatment for concrete mix design at various substitution percentages as coarse aggregates. The experimental investigation further progresses with the evaluation of mechanical and durability properties of concrete mixes, which is additionally followed by microstructural studies such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetry-differential thermal analysis (TG-DTA). The outcomes demonstrate that two-stage treatment, such as mechanical abrasion followed by sodium silicate immersion, yields superior-quality RA. Recycled aggregate concrete (RAC) made with these treated aggregates illustrated an increase in workability and density with respect to an untreated RAC mix. Furthermore, comparable strengths in compression, flexure, and tension are found in treated RAC mixes, particularly at 35% replacement levels, with respect to concrete mixes comprised of natural aggregates. A similar trend is detected in the chloride penetration tests and water sorptivity tests. In addition, the microstructural investigation confirmed the formation of additional calcium silicate hydrate for treated RAC mixes, particularly for the 35% substituted RA mix. On the basis of the results, it is suggested that multi-stage jaw crushing followed by treatment through mechanical abrasion and sodium silicate can potentially enhance the mechanical, microstructural, and durability performance of RAC.

The role of ultra-fine supplementary cementitious materials in the durability and microstructure of airport pavement concrete

Conventional Supplementary cementitious materials (SCMs) are indispensable constituents of high-performance concrete, despite their potential drawback of reducing the early strength of concrete. Ultra-fine supplementary cementitious materials (USCMs) have been employed to expedite the pozzolanic reaction and refine micro-scale particle gradation in airport pavement concrete. The investigation encompassed an assessment of mechanical properties, durability, phase assemblage, pore structure, morphology, and microstructure. Results showed that the incorporation of USCMs significantly enhanced the flexural and compressive strength of concrete during the early age, exhibiting respective improvements of 25.4% and 12.8%, respectively. Moreover, the freezing-thawing resistance was enhanced by a factor of 1.6, and the chloride penetration resistance was improved approximately 4 times. These enhancements can be attributed to the heightened pozzolanic and filling effects of USCMs, which resulted in the consumption of more calcium hydroxide (CH) at 7 d and facilitated the growth of additional calcium silicate hydrate (C-S-H) gel, along with lowering hydration heat and decreasing remarkably porosity. Notably, the incorporation of USCMs led to a considerable improvement in the volume fraction of harmless pores (with pore diameter ≤ 50 nm), optimizing the pore structure of the concrete and thereby augmenting its mechanical properties and durability.

Experimental Study on Partial Replacement of Cement with Nano Silica

Cement is a building material made by grinding calcined limestone and clay to a fine powder, which can be mixed with water and poured to set as a solid mass. However it is expected that the use of Nano-silica in concrete improve the strength properties of concrete. Nano silica is used in concrete to enhance its properties such as compressive strength and tensile strength. When added to concrete, nano silica particles react with the calcium hydroxide to form additional calcium silicate hydrate, which helps to improve the concrete's strength. This can result in concrete with improved resistance to cracking and corrosion, and with a longer service life.An experimental objective has been carried out by replacing the cement with Nano silica by 0%, 0.5%,1.0%, 1.5%, 2.0%, 2.5% for M30 grade of concrete. The test conducted on it shows a considerable increase in early-age compressive strength and a Split Tensile strength of concrete on 7th day, 14th day and 28th day of curing. The final outcome of the project will have an overall beneficial effect on the utility of Nano-silica concrete in the field of civil engineering construction work.

A review on the properties of recycled aggregate concrete (RAC) modified with nano-silica

The present study reviews the properties of recycled aggregate concrete (RAC) modified with nano-silica (nS). It has been observed in previous studies that the RAC possesses weaker mechanical properties as compared to natural aggregate concrete (NAC). There are many interfacial transition zones (ITZs) present in RAC. Several attempts have been made in the past to use some mineral additives in the RAC to enhance its mechanical performance. The use of nS is one such choice in this regard. nS possesses high filling ability due to its very small size. It can fill the micro and nano-sized pores and cracks present in RAC. It also improves the weak ITZs. It also has high pozzolanic activity. It reacts with the calcium hydroxide formed during the cement hydration and, in turn, produces additional calcium silicate hydrate (CSH) gel. This additional CSH gel densifies the microstructure of RAC. It is found that the synergistic effect of the two factors, that is, high filling ability and high pozzolanic activity of nS improves the internal structure of the RAC and is responsible for the enhancement of RAC’s properties. It has been observed that the incorporation of nS into the RAC results in a concrete whose strength is comparable to the strength of NAC.

Creep of concrete incorporated with marble powder

This study presents an experimental investigation of the mechanical properties of concrete incorporating Kadapa Marble Powder (KMP) as an additional cementitious material. It focuses on varying the content of KMP (ranging from 0% to 15% by weight of cement) and conducting tests on compressive strength, modulus of elasticity, and creep. The replacement of cement with KMP led to improvements in the compressive strength and modulus of elasticity, and the incorporation of KMP contributed to a reduction in the creep phenomenon of concrete over time. The beneficial effects of KMP can be attributed to its ability to react with calcium hydroxide generated during cement hydration. This reaction results in the production of additional calcium silicate hydrate, which fills voids and large pores within the concrete matrix. As a result, the porosity associated with the capillary pores and voids decreased. This observation was supported by the examination of the microstructure of hardened concrete using scanning electron microscope techniques. The presence of KMP enhanced cement hydration and contributed to a reduction in the porosity associated with the gel pores. This was attributed to the release of absorbed water retained in the small pores of the KMP particles. This study highlighted the potential of incorporating KMP as a beneficial cementitious material for concrete production. These findings suggest that KMP can enhance the mechanical properties of concrete, including the compressive strength and modulus of elasticity, while mitigating the creep phenomenon. The analysis also provides insights into the microstructural changes that occur in concrete due to the inclusion of the KMP.

Strength properties of ordinary Portland cement concrete containing high volume recycled coarse aggregate and volcanic ash

Due to the increasing demand and declining reserve of natural coarse aggregate, waste recycling is one of the most viable options for sustainable development in concrete production. The paper assessed the compressive and tensile strength of ordinary Portland cement concrete containing high-volume recycled coarse aggregate (RCA) and volcanic ash (VA). Concrete of grade 60 was designed using the Department of Environment (DoE) method of mix design to produce concrete cubes of 100 × 100 × 100 mm and cylinders of 200 × 100 mm using a water/binder ratio of 0.35. The recycled coarse aggregate concrete (RCAC) was produced using ordinary Portland cement, 15% VA, 100% recycled coarse aggregate (RCA), natural fine aggregate and water while the conventional concrete was produced using ordinary Portland cement, natural fine and coarse aggregate, and water. The hardened concrete cubes and cylinders were subjected to compressive and tensile strength at 7, 14, 28, 56, and 90 days. The microstructure of the concrete samples was also evaluated. Results obtained from the study showed that the conventional concrete had higher compressive strength than the RCAC by 12.8% and 7.12% at 28 and 56 days respectively. However, at 90 days, RCAC attained higher compressive strength than conventional concrete by 1.5%. Similarly, the conventional concrete had higher tensile strength than RCAC by 12.87% and 6.45% at 28 and 56 days respectively. At 90 days, RCAC attained higher tensile strength than that of conventional concrete by 4.55%. Higher compressive and tensile strength improvement at 90 days exhibited by RCAC was due to the pozzolanic reactivity of VA which yielded additional calcium silicate hydrate (C-S-H) at a later age. It is recommended that up to 100% of normal coarse aggregate could be replaced with recycled coarse aggregate especially when pozzolanic material (VA) is to be added.

Evaluation of pozzolanic activity, heterogeneous nucleation, and microstructure of cement composites with modified bentonite clays

The use of bentonite clays as supplementary cementitious material (SCM) is limited because of their low pozzolanic activity, high hydrophilicity, and dramatic swelling nature. In this study the bentonite clay was modified by silane treatment, and its pozzolanic activity was compared with as-received bentonite (ARB) and calcined bentonite (CB) clays. Portlandite quantification by thermogravimetry and Rietveld analysis showed a higher pozzolanic activity of the silane-modified clay. The specific surface area (SSA) of silane-treated bentonite (STB) clay was increased by 314% than ARB clay which provides an additional surface for the heterogeneous nucleation of cement hydrates, thereby improving the microstructure of the cement paste. The hydrolysis and polycondensation of silane on the surface of the STB clay generates SiO2 like structure which reacted with portlandite to produce an additional calcium silicate hydrate (C-S-H). The swell index and hydrophilicity of the STB clay were significantly reduced, which improved the mortar flow and mechanical strength.

EXPERIMENTAL STUDY OF CONCRETE WITH SUGARCANE BAGASSE ASH (SCBA) AT ELEVATED TEMPERATURE

The partial incorporation of natural pozzolans like sugarcane bagasse ash in concrete construction is of the prominent attention to meet the high demand for cement while also ensuring a sustainable environment. The sugarcane bagasse ash has higher percentages of silica compared to ordinary Portland cement (OPC). When sugarcane bagasse ash undergoes pozzolanic reaction, additional Calcium Silicate Hydrate (C-S-H) is formed in cement hydration matrix. This study concentrates on the effectiveness of using sugarcane bagasse ash (SCBA) as a cement substitute in concrete at prolonged elevated temperatures. For investigation different compositions of SCBA (5%, 10% and 15%) were added to the concrete with a water-cement ratio of 0.49. The compressive strength of the test samples was investigated at room temperature (26°C) for reference performance along with the several elevated temperatures of 60°C, 120°C, 180°C, and 240°C for two hours. Afterward, the concrete efficiency was assessed considering the residual compressive strength. The result shows an improvement of compressive strength up to 10% SCBA inclusion at room temperature. Moreover, concrete specimens which are exposed to elevated temperatures exhibit a notable decrement of compressive strength. However, the descending rate of compressive strength was low in case of SCBA concrete compare to other pozzolanic mixture. A 10% substitution of cement with sugarcane bagasse ash (SCBA) demonstrated most observable mixing in concrete considering cost effectiveness and resistance against elevated temperatures.

Study of mortar layer property of superhydrophobic metakaolin based cement mortar

The use of alternative materials of cement to prepare cement-based materials has attracted more attention to promote the low-carbon and sustainable development in the field of civil engineering. A clean and sustainable method was proposed of preparing cement mortar using metakaolin as an alternative material with suitable mortar layer property. Superhydrophobic metakaolin (SMK), prepared by using a safe and non-toxic method, was added into cement mortar, and its effects on the of the cement mortar layer was investigated. The SMK was found to improve the thickness of the mortar layer and adhesion ability. The SMK increased the cohesiveness of the cement mortar and improved the stability of the mortar layer, thereby increasing the thickness of mortar layer. The results of TGA and SEM show that the SMK rate with less than 2% promoted the hydration of cement, produced additional calcium silicate hydrate and ettringite, and improved the interface transition zone between the aggregate and the cement mortar layer, thereby improving the cement mortar adhesion ability to the aggregate. It is expected that the proposed method may expand the application of superhydrophobic metakaolin in cement-based materials.

Role of barium carbonate and barium silicate nanoparticles in the performance of cement mortar

This study investigates the impact of low-cost barium carbonate and barium silicate nanoparticles (NBC and NBS, respectively) on the performance and phase composition of cement mortar (CM). The results reveal that the individual addition of NBC and NBS causes setting times shortening and mechanical properties increment. Nevertheless, the NBS exhibits the higher efficiency at all addition levels (1, 2, and 3% by weight of cement). The incorporation of NBC results in the consumption of sulfate within cement matrix and the formation of insoluble barite (BaSO4) and calcium monocarboaluminate phases. Although the NBS also represents high efficiency in the uptake of sulfate, the reactive silicate within NBS plays a significant role in the formation of additional calcium silicate hydrate content through the consumption of portlandite (resulted from cement hydration). This could enhance the successful application of cement-NBS mixtures as super sulfate resistant cements.

Effect of Combined Supplementary Cementitious Materials on the Fresh and Mechanical Properties of Eco-Efficient Self-Compacting Concrete

Global concrete demand is causing depletion of natural resources at an alarming rate. Self-compacting concrete (SCC) is an innovative solution as it uses less aggregates; however, the drawback of SCC is that high cement content is required compared to conventional concrete. Considering that cement production emits 7% of carbon dioxide (CO2) gas emissions, the use of high content of cement in SCC production is concerning. Though the high powder content of SCC may be of a concern, however, it allows the opportunity to substitute the cement content with supplementary cementitious materials. This experimental work was therefore conducted to reduce the cement content by substituting it with waste materials, such as eggshell powder (ESP) and palm oil fuel ash (POFA), and develop an eco-efficient SCC. The cement content was partially substituted by 0 to 5% ESP and 0 to 15% POFA by weight of total binder. A total of 90 cubes of 100 mm and 60 cylinders of 100 × 200 mm dimension were prepared to evaluate the compressive and splitting tensile strengths, modulus of elasticity, and Poisson’s ratio. Furthermore, the environmental impact assessment was conducted to assess the embodied CO2 and eco-strength efficiency of the developed eco-efficient SCC. It was found that the combination of POFA and ESP increased pozzolanic reactivity, developing additional calcium silicate hydrate gels, thus increasing strength. The combination of 2.5% ESP and 5% POFA (a total of 7.5% cement substitution) was deemed to be the optimal combination as it provided better strength in SCC after 28 days of curing, which leads to 9.66% higher compressive strength than the control SCC. Furthermore, the developed SCC was observed to be eco-friendly as it reduced embodied carbon ranging from 3.86 to 15.33% and eco-efficiency ranging from 2.38 to 15.48% on 28 days compared to the control SCC.

Influence and mechanisms of active silica in solid waste on hydration of tricalcium aluminate in the resulting composite cement

Many industrial solid wastes are rich in silica (SiO2) which can be used as supplementary cementitious material (SCM) to replace part of Portland cement. Existing studies mainly focus on the impact of solid waste on tricalcium silicate (C3S) hydration. Since tricalcium aluminate (C3A) is the most reactive component of the Portland cement, it is of great interest t to investigate the effect of solid waste containing SiO2 on the hydration process of C3A. In this study, different amounts of nano-silica (nano-SiO2) were mixed with C3A and the hydration products after 72 h of hydration were analyzed by means of X-ray diffraction (XRD), Fourier Transform Infrared analyzer (FT-IR), Environment Scanning Electronic Microscope - Energy Dispersive Spectrometer (ESEM-EDS), X-ray Photoelectron Spectroscopy (XPS) and Solid-state Nuclear Magnetic Resonance (NMR). The results showed that nano-SiO2 can promote the hydration of C3A and stabilize the hydration products of C3A in the form of crystalline hydrogarnet (C3AH6). The formation of Si-O-Al bonds was also found in the hydration products. ESEM results revealed that the surface of the crystalline hydration products (C3AH6 particles) was covered by gel-like products. The results from the XPS and NMR analyses further confirmed that the negatively charged nano-SiO2 and the silicate anions can literally interact with C3A to produce calcium silicoaluminate hydrate (C-A-S-H) gel, whereas the formation of C-A-S-H is attributed to the substitution reaction of Al in the Si-O-Si network occurring on the surface of C3A. In addition to the reactive silica-aluminum component reacting with Ca(OH)2 to form additional calcium silicate hydrate (C-S-H) and C-A-S-H gels, the reactive silicon in solid waste can also undergo pozzolanic reaction with C3A to form C-A-S-H gel.

Effects of a Portland cement additive rich in SiO2 and Al2O3 in microstructure densification of RAP incorporated RCCP mixes

Past studies shows that the introduction of extra calcium silicate hydrate (C-S-H) gels, by means of various supplementary cementitious materials, did not show much significant effect on the strength of the roller compacted concrete pavement (RCCP) mixes made with reclaimed asphalt pavement (RAP) aggregates. Therefore, this paper is an attempt to refine the pores of RAP-RCCP mixes by inducing filler effect with the help of SiO2 and Al2O3 particles, derived by means of a Portland cement additive. The incorporation levels of the additive were 0, 2, 4, 6, 8, and 10%, respectively, which were introduced into the RCCP mixture containing 50% RAP aggregates (R-50 mix). Based on the scanning electron microscope images, it was observed that the asphalt cohesion failure was prevalent although the additional calcium silicate hydrate gels were able to refine the microstructure of the mortar paste. However, improvement in the pore structure of the RAP-RCCP mixes was observed as the SiO2 content increases. Moreover, the presence of Al2O3 particles could also react with the calcium carbonate present in the concrete (as shown by x-ray diffractometer patterns) to produce hemicarboaluminate and monocarboaluminate which could act as a filler and densify the interfacial transition zone of the RAP concrete. This promising effect was observed when the additive was utilized in a proportion of 10% wherein a marginal enhancement of 2–7% was observed in the compressive, flexural, and split tensile strength of the R-50 mix. In fact, the calcium aluminate hydrate phases formed on reaction between the Al2O3 particles and the calcium hydroxide could also induce higher progression reaction within initial days itself. Meanwhile, the relationships established in the present study also indicated a strong relation co-exists between the compressive and flexural strength, and compressive strength and the abrasion resistance as well.

High Volume Slag and Slag-Fly Ash Blended Cement Pastes Containing Nano Silica

This paper presents the effect of nanosilica (NS) on compressive strength and microstructure of cement paste containing high volume slag and high volume slag-fly ash blend as partial replacement of ordinary Portland cement (OPC). Results show that high volume slag (HVS) cement paste containing 60% slag exhibited about 4% higher compressive strength than control cement paste, while the HVS cement paste containing 70% slag maintained the similar compressive strength to control cement paste. However, about 9% and 37% reduction in compressive strength in HVS cement pastes is observed due to use of 80% and 90% slag, respectively. The high volume slag-fly ash (HVSFA) cement pastes containing total slag and fly ash content of 60% exhibited about 5%-16% higher compressive strength than control cement paste. However, significant reduction in compressive strength is observed in higher slag-fly ash blends with increasing in fly ash contents. Results also show that the addition of 1-4% NS improves the compressive strength of HVS cement paste containing 70% slag by about 9-24%. However, at higher slag contents of 80% and 90% this improvement is even higher e.g. 11-29% and 17-41%, respectively. The NS addition also improves the compressive strength by about 1-59% and 5-21% in high volume slag-fly ash cement pastes containing 21% fly ash+49%slag and 24% fly ash+56%slag, respectively. The thermogravimetric analysis (TGA) results confirm the reduction of calcium hydroxide (CH) in HVS/HVSFA pastes containing NS indicating the formation of additional calcium silicate hydrate (CSH) gels in the system. By combining slag, fly ash and NS in high volumes e.g. 70-80%, the carbon footprint of cement paste is reduced by 66-76% while maintains the similar compressive strength of control cement paste. Keywords: high volume slag, nanosilica, compressive strength, TGA, high volume slag-fly ash blend, CO2 emission.

Effect of nano silica on compressive strength and microstructures of high volume blast furnace slag and high volume blast furnace slag-fly ash blended pastes

This paper presents the effect of nano silica (NS) on compressive strength and microstructure of cement paste containing high volume blast furnace slag (BFS) and high volume BFS-fly ash (FA) blend as partial replacement of ordinary Portland cement (OPC). Results show that high volume BFS pastes containing 60% and 70% BFS exhibited 4% higher and comparable compressive strength, respectively than control cement paste. However, about 9% and 37% reduction in compressive strength in high volume BFS pastes is observed due to use of 80% and 90% BFS, respectively. The high volume BFS-fly ash pastes containing total BFS and FA content of 60% exhibited about 5%–16% higher compressive strength than control cement paste. However, significant reduction in compressive strength is observed in higher BFS-FA blends with increasing fly ash contents. Results also show that the addition of 1–4% NS improves the compressive strength of high volume BFS paste containing 70% slag by about 9–24%. However, at higher BFS contents of 80% and 90% this improvement is even higher e.g. 11–29% and 17–41%, respectively. The NS addition also significantly improves the compressive strength of high volume BFS-FA pastes. The thermogravimetric analysis (TGA) results confirm the reduction of calcium hydroxide (CH) in high volume BFS and combined BFS-FA pastes containing NS indicating the formation of additional calcium silicate hydrate (CSH) gels in the system. The addition of NS also significantly reduced the pore volume of high volume BFS and combined BFS-FA pastes. The X-ray diffraction (XRD) analysis also confirms the reduction of intensity of CH peaks indicating its consumption in pozzolanic reaction. The scanning electron microscopy (SEM) images also confirm denser microstructure of high volume BFS and combined BFS-FA pastes containing NS compared to those without NS. By combining slag, fly ash and NS in high volumes e.g. 70–80%, the carbon footprint of cement paste is reduced significantly while maintains the similar compressive strength of control cement paste.

Effect of colloidal nanosilica on early-age compressive strength of oil well cement stone at low temperature

The compressive strength of cement stone rises slowly when cementing marine shallow section at low temperature, resulting in increased drilling cost and risk. This paper presents results of experimental study that was conducted to investigate the effect of low temperature on early-age compressive strength of cement stone admixed with colloidal nanosilica. The compressive strength of cement stones was measured after aging at 4 °C for 1, 3, and 7 days respectively. The hydration products of different aging cement stone were analyzed by X-ray diffraction and Fourier Transform infrared spectroscopy, and the microstructures were observed by scanning electron microscopy. In addition, the hydration exotherm of colloidal nanosilica modified cement slurry during hydration process was tested at 20 °C. The results indicated that the compressive strength of cement stone significantly improved by colloidal nanosilica. Interestingly, colloidal nanosilica retarded the initial hydration, and then promote the hydration process afterward. The mechanism of colloidal nanosilica to improve the compressive strength of cement stone was that colloidal nanosilica consumed calcium hydroxide to produce additional calcium silicate hydrate, filling large pores and cracks inside cement stone. More importantly, nanosilica particles provided nucleation sites of cement hydration and modified the internal structure of the hardened stone. The improvement of early-age compressive strength of oil well cement stone is beneficial to saving costs and reducing risk.

Strength and Microstructural Properties of Mortar Containing Soluble Silica from Sugarcane Bagasse Ash

Sugarcane bagasse is among the abundantly available waste in agriculture industry. The proportion of siliceous ashes after the incineration process is one of the attractive features in sugarcane bagasse. However, its low bulk density would result in an additional issue for further use as cement replacement material, since higher replacement volume will bring more hydrophilic particles of sugarcane bagasse ash into the mixture. Therefore this research aims to extract the reactive silica from sugarcane bagasse ash and increase its bulk density by converting it into soluble form. The process was divided into three stages, which were pre-treatment and incineration of sugarcane bagasse, conversion into soluble form, and production of mortar specimen. Soluble silica from sugarcane bagasse ash was used to partially replace cement content in mortar, hence its effect on the hydration process can be evaluated. Compression test and scanning electron microscope analysis were performed to observe its effect on the strength and microstructural development of mortar framework. The results show that the inclusion of soluble silica would enhance the early hydration rate and improve the consolidation of cement matrix via additional calcium silicate hydrate formation, which would increase the capability of internal mortar framework to distribute loads and achieve higher strength.