Compressive Strength Of Cement Paste Research Articles

Assessment of blended cement containing waste basalt powder: physicomechanical and electrochemical impedance spectroscopy investigations

Basalt powder (BP) is the residue of a plant that crushes basalt stones. This work deals with the effect of waste BP on the properties of cement mortars and the physical properties of hardened mortars. Modified concrete was prepared by partial replacement of BP in amount of 5, 10, 20% by weight of cement. Physico-mechanical properties and corrosion resistance were investigated. Electrochemical impedance spectroscopy (EIS) was used to examine the corrosion behavior of cement pastes with a partial addition of basalt powder in aggressive solutions of 5% NaCl and 5% MgCl2 for up to 270 days. Infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were also performed to investigate the hydration process and microstructure formation of the basalt blended paste. Results indicate that the addition of basalt powder as a partial replacement of cement influences the microstructure of the interfacial transition zone (ITZ), which is denser and stronger than in cement paste without basalt powder. The filler effect of the basalt powder improves the compressive strength of cement paste. Also, comparing BP0 and BP20 in 5% NaCl after 270 days, the partial substitution of cement with BP resulted in a higher compressive strength of 671 and 895 kg/cm2, respectively. The EIS results also showed the highest values of Rp 953 ohms cm2 after 270 days. This high corrosion resistance might indicate the binding by high Al2O3 that reduced the free aggressive chloride ions in the solution.

A new hypothesis for full stage deformation of cement-based materials mixed with MgO expansive agent: Generation and filling of cavity

MgO expansive agent (MEA) is an effective admixture for compensating for shrinkage and minimizing cracking in concrete. This study reexamined prevailing explanations of its expansion mechanism, with a particular focus on the synergetic influence on early-age compressive strength. Full-stage deformations and compressive strength of cement pastes with different reactivities and dosages of MEAs were investigated. Four deformation stages were uncovered, and the correlation among deformations and pore structures was systematically analyzed from the standpoint of expansion driving forces. Particular attention was given to the generation of cavity and swelling pressure due to the unique physicochemical properties of fine brucite for water adsorption. Swelling pressure was used to explain the sharp increase in expansion and decrease in strength of cement pastes at early ages, and crystallization pressure was used to account for shrinkage compensation and strength enhancement of MEA at late ages. A new hypothesis, based on the generation and filling process of cavity varying with the reactivity and dosage of MEA, was proposed to describe the expansion mechanism of cement pastes mixed with MEA.

Machine learning for predicting compressive strength of sustainable cement paste incorporating copper mine tailings as supplementary cementitious materials

Copper mining produces significant amounts of copper mine tailings (CMT), necessitating appropriate waste handling and disposal practices. By substituting a portion of cement with CMT as supplementary cementitious materials (SCMs), we aim to address two environmental issues simultaneously: reducing copper mine waste in landfills and decreasing embodied carbon by using less cement. The exploration of CMT recycling as a cement replacement requires evaluation of its impact on material performance, such as compressive strength. In this paper, we address this by machine learning that features data fusion of large public data with our own small data on compressive strength of CMT-incorporated cement. We developed and critically evaluated three machine learning models: a simple linear model, Gaussian process, and random forest that predict the compressive strength of CMT-incorporated cement pastes with different mix designs (e.g., varying amounts of CMT and water-binder ratios) and curing ages. Hyperparameters in the random forest model were tuned using Bayesian optimization. Following a comprehensive evaluation of the models, we find that the random forest model can accurately estimate the compressive strength of cement paste across the mix designs. Furthermore, results from SHapley Additive exPlanation (SHAP), Individual Conditional Expectation (ICE), and Partial Dependence Plots (PDP) revealed that cement, ground-granulated blast furnace slag, superplasticizers, and curing ages positively influence compressive strength. This study contributes to acceleration of sustainable material technology to obtain the best mix design and desired compressive strength.

Role of C-F-S-H/PCE nanocomposites on the hydration of Portland cement with varying gypsum levels

This study delves into the role of C-F-S-H/PCE (calcium-ferrite-silicate-hydrates/polycarboxylate ether) nanocomposites on the cement hydration with varying gypsum levels. It is found that the addition of C-F-S-H/PCE nanocomposites simultaneously promotes the dissolution of cement clinker and gypsum during early hydration. What’ more, the early hydration is further enhanced notably by C-F-S-H/PCE nanocomposites at moderately higher gypsum level without compromising the long-term compressive strength. It merits attention that the compressive strength of cement paste emerges as a factor intricately interwoven with not only its microstructure but also the content of AFt (ettringite) it harbors. Anyway, in the presence of the C-F-S-H/PCE nanocomposites, the faster depletion of gypsum leads to an earlier formation of AFm (monosulfoaluminate) whereas the morphologies of various hydration products remain unaffected. The findings demonstrate that the addition of C-F-S-H/PCE nanocomposites increases the demand for gypsum in cement and provide insights into the production of cement and concrete using seeding materials.

Effects of Noncrosslinked Polyvinyl Alcohol Fluid Loss Additive on the Compressive Strength and Viscosity of Class G Cement Slurries

Summary Limiting the fluid loss from the cement slurry to the adjacent formation by using additives is essential for maintaining the slurry’s water/cement ratio. The present work focuses on the effect of noncrosslinked polyvinyl alcohol additive (PVOH), a widely used fluid loss additive (FLA), on the compression strength and rheological behavior of Class G cement pastes. Results of the current study show that the PVOH surfactant characteristic and its absorptive mechanism interfere not only with the hydration process but also with the physical properties and compressive strength of cement pastes, such as porosity, permeability, and early age strength, which revealed the importance of using a defoamer when PVOH is present in the mixture. In the absence of a defoamer, the PVOH additive generates foam in the mixed cement paste samples, which results in increased porosity and reduced compressive strength of the hardened cement paste. Moreover, regarding rheology, increasing the PVOH concentration increased the effective viscosity when evaluating flow curves. Therefore, this study demonstrates a systematic method for assessing the possible effects of cement paste additives, such as PVOH and defoamer, providing a physical and mechanical approach rather than just chemical to evaluate additives’ influence on the mixtures. This method should consider different additives in combination with PVOH to test cement paste stability and to obtain specific working recipes.

Comparison between Four-Probe and Two-Probe Electrical Resistivity Measurement to Monitor the Curing and Piezoresistivity Behavior of Smart Cement Paste Modified with Waste Steel Slag and Green Nano-magnetite

Abstract This study aims to examine the compressive strength, electrical resistivity, and piezoresistivity characteristics of ordinary Portland cement (OPC) with a constant water-to-cement ratio (w/c) of 0.38. The optimal value of steel slag (SS) was determined to be 5 % based on the compressive strength of six different mixes of cement paste modified with various SS from 0 % to 30 % weight of cement. Additionally, the investigation will include modified cement samples containing 1 % green synthesized material and commercially available nano-magnetite (NM). Because iron is the primary component of SS and NM, the electrical resistivity, which is the primary criterion for structural health monitoring of cementitious material, can be increased by adding SS and NM. Hence, a comparative analysis was conducted to assess the resistivity of cement paste throughout the early curing period up to 28 days using an alternative current (AC) and embedding wires into the specimen, employing both the two-probe (2P) and four-probe (4P) methodologies. The findings suggest that the 4P method is a more precise approach for determining electrical resistivity than the 2P method, as the wire probe is not considered in the 4P method. Hence, it is imperative to compute the correlation between the 2P and 4P methodologies in order to attain a precise resistivity measurement. The suggested model indicates that the expected 4P resistivity can be measured with high precision, a high coefficient of determination (R2) of .97, and a low root mean square error (RMSE) of 7.33 Ω·m, based on the 2P result. The piezoresistivity results demonstrated that the cement paste modified with green synthesis nano-magnetite (GSNM) had a higher electrical resistivity (ER) change, 10.85 % greater than cement paste only, 57 % higher than cement modified with SS, and 34.2 % higher than cement paste modified with commercial nano-magnetite (CNM) after 28 days of curing. In addition, the compressive strength of cement paste modified with GSNM was higher than that of cement paste, cement paste modified with SS, and cement paste modified with CNM by 15.96 %, 21 %, and 1.7 %, respectively, after 28 days of curing. A Vipulanandan p–q model was used to forecast the electrical resistivity of cement paste versus time at start hydration during 28 days of curing and the change of electrical resistivity versus compressive strength at 3, 7, and 28 days. The Vipulananda p–q model anticipated both electrical resistivity and piezoresistivity behavior well.

Algal Biochar-Metal Nanocomposite Particles Tailor the Hydration Kinetics and Compressive Strength of Portland Cement Paste.

Biochar can improve the mechanical properties of portland cement paste and concrete. In this work, we produced algal biochar-zinc (biochar-Zn) and algal biochar-calcium (biochar-Ca) nanocomposite particles and studied their effect on the hydration kinetics and compressive strength of cement paste. Results show that 3 wt % biochar-Zn delayed peak heat evolution during cement hydration from 8.3 to 10.0 h, while 3 wt % addition of biochar-Ca induced a minor acceleration of peak heat from 8.3 to 8.2 h. Both biochar-Zn and biochar-Ca nanocomposite particles increased the compressive strength of cement paste at 28 days by 22.6 and 17.0%, respectively. Data substantiate that retardation or minor acceleration of the reaction kinetics was due exclusively to the presence of Zn and Ca phases, respectively, while the enhanced strength was attributed to a nucleation effect induced by such phases and the internal curing effect of biochar.

Effect of Superabsorbent Polymer (SAP) Size on Microstructure and Compressive Strength of Concrete.

Superabsorbent polymers (SAPs) are hydrophilic, polymeric network materials renowned for their ability to enhance various properties of cementitious materials. This investigation examines the impact of SAP size on the hydration degree, porosity, and compressive strength of cement pastes and concrete under diverse curing conditions and ageing periods. The findings reveal that SAP addition stimulates the hydration of the C2S phase, particularly during the early curing stages, thereby favouring early strength development. However, the effect of SAPs on hydration promotion diminishes as their size increases. Conversely, the size of SAPs affects the hydration range of their action, and the 400 µm SAP demonstrates the most extensive range of hydration enhancement, reaching up to 105 µm. Additionally, SAPs effectively reduce porosity in small pores (4 nm-10 μm), with 200 μm and 400 μm SAPs exhibiting the highest efficacy. While analysing the effects of SAPs on larger pores (>10 μm), the results show that although larger SAPs result in larger average porosity, the total porosity is effectively reduced, particularly in samples incorporating 400 μm SAP. The compressive strength of cement paste, even after 28 days, is slightly reduced following the introduction of SAPs. However, the strength of concrete, due to the naturally occurring pores eliminating the negative effects of the pores produced by SAPs, is significantly increased following the introduction of SAPs, especially 400 µm SAP.

In-situ dispersion of nano-TiO2 to highly reinforce cement paste

Regardless of how good pre-dispersion of nano-TiO2 in aqueous solutions, re-aggregation rapidly occurs once it is mixed into fresh cement mixtures, limiting the nano-reinforcing efficiency for cement-based materials. In this study, an in-situ release strategy by pre-encapsulating nano-TiO2 in microscaled ice and post-dispersing into fresh cement matrix during ice-melting process was developed to highly reinforce the microstructure and properties of cement paste. Compared with the conventional dispersion strategy, a much better dispersion of nano-TiO2 (0.6 wt% by cement) was achieved using the in-situ release strategy, which not only improved the 7- and 28-day compressive strength of cement paste by 9.2% and 10.1%, respectively, but also reduced the cement hydration heat and water adsorption by 36.1% and 4.6%, respectively. In addition to this, the NO degradation efficiency of cement paste was also improved by 20% due to the larger exposed surface area of nano-TiO2 with better dispersion. These research outcomes demonstrate that the in-situ release strategy facilitates the dispersion of nano-TiO2 in cement matrix and contributes to highly reinforcing cement paste with lower hydration heat and water adsorption, strong mechanical strength and higher photocatalytic properties.

Internal curing with superabsorbent polymer modified by nano SiO2: Shrinkage mitigation and microstructure refinement

The existing commercial superabsorbent polymer (SAP) products have the intrinsic defects of low internal curing efficiency and weakening strength. In this paper, a novel type of organic-inorganic composite SAP (SAPN) modified by nano SiO2 was designed and synthesized. The absorption-desorption kinetics of SAP-N in alkali pore solution were measured to evaluate the structural stability and water retention capacity. The water transport process and distribution of SAP-N in cement pastes were studied using 1H NMR and X-ray computed tomography. In addition, the effect of SAP-N on the autogenous shrinkage, microstructure, and compressive strength of cement pastes was investigated. The research results demonstrated that the incorporation of nano SiO2 could enhance the absorption capacity of SAP in pore solution. The water retention capacity of SAP-N was increased by over 50 % compared to commercial SAPC, despite the dissolution of a proportion of nano SiO2. SAP-N exhibited a low agglomeration degree but a high effective utilization rate of internal curing water in cement pastes, and thus mitigated effectively the self-desiccation and autogenous shrinkage. The hydration degree of cement pastes internally cured with SAP-N was significantly enhanced owing to the pozzolanic effect of nano SiO2, which enabled the in-situ repair of residual voids and reduced capillary pore size, thus improving the long-term compressive strength.

Comparative study of nanomaterials activated recycled powders from demolition and decoration wastes as supplementary cementitious material

Powdered particles can significantly affect the technical performance of recycled aggregates and recycled concrete. Therefore, there has been a considerable focus on the disposal and utilization of recycled powder (RP) with high value. This study applied nano-CaCO3 (NC), nano–graphene oxide (GO) and nano–SiO2 (NS) to activate RP from demolition and decoration waste (RP1 and RP2, respectively). The results indicated that the nanomaterials had an activation effect on RP, but the effect was more pronounced for RP2. In addition, NC had the best activation effect on the RP among the three nanomaterials. Comparing to cement pastes with 30% RP2, compressive strength of cement paste activated by NC, GO, and NS were increased by 43.4%, 33.3% and 23.7% at 28d, respectively. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning electronic microscopy (SEM), and mercury intrusion porosity (MIP) were utilized to further explore the activation mechanism. Results presented that nanomaterial activated RP could promote hydration degree to produce more Ca(OH)2 (CH), meanwhile, the nanomaterials activated RP refine and modified the orientation index of CH. This paper implies a useful activation method for RP, which is expected to fully stimulate the potential of RP to form new kinds of supplementary cementitious material.

Comparative study on the environmental impact of Portland cement paste that mixed with naphthalene or carboxylate based polymer solutions

The environmental impact is now a valuable coefficient for any human activity. The effect of solar UV radiation on the cement samples was limited and contained in the thin surface layer of the samples. In general, viscocrete was the most effective in protecting cement against solar ultraviolet radiation, where cement samples treated with the two polymers used separately showed greater compressive strength values than those recorded for samples treated with sikament polymer. This study is important since the mechanical properties of cement and concrete at early stages are important in the field of civil engineering. The effect of soaking in water on the ability of the cement to withstand the pressure on it was also studied, and several physical measurements were applied to samples of untreated cement and samples mixed with the mentioned polymers. These measurements included measuring the porosity, density, and total dissolved solids by X-ray diffraction, FTIR, and line scan EDX. These measurements were carried out on cement samples before, after, after soaking in water, as well as on cement samples mixed with polymers. The measurements were extended to the soaking water. So, adding two types of polymers (Sikament and Viscocrete) separately to cement could protect concrete constructions against serious environmental impacts. The EDX analysis of the samples used in this study showed that the Egyptian sources of raw materials used in the cement industry are rich sources of rare chemical elements. The importance of adding two types of polymers, Sikament and ViscoCrete, separately to cement protects concrete construction against environmental impacts, which is our main highlight, significance, and advice of this work. Decrease the water reduction percentage and increase the compressive strength for portend cement paste to 0.5 % viscocrete using 15 W and 30 W UV lamps, with a maximum value of 127.52 MPa for 0.5 % viscocrete at the 30 W lamp. Higher UV lamp exposure at 45-watt lamp decreases the compressive strength after exposure than others. The total porosity percentage of all used percentages of Sikament polymer addition is greater than that using viscocrete polymer with a 0.75 % Sikament high value of 7.60 (total porosity) TP%. The conductivity EC of the cement treated with polymer samples shows a smaller increase in the case of viscocrete polymer than that of Sikament, with a value of 404 uS using 0.5 % and 0.75 % viscocrete, which is supported by TdS measurements with values of 202 ppm for 0.5 % and 0.75 % viscocrete, respectively. The EDX results for cement polymer mixtures prove that both polymers used extract many elements from the cement paste and protect human beings from their dangers, like Sb, Na, Zr, Hf, Rb, Mo., Ti, P, Cu, Er, Cl, In, and Te,Te with greater efficiency for the Viscocrete polymer than the Sikament one. Many factors affecting the cement's compressive strength and mechanical properties are the innovation of this work, which deals with the impact of some materials affecting it. The main target is to discuss the effect of different polymers on some properties of cement paste. Other properties can be discussed in near future, like the void volume effect, packing density, Van der Waals volume, and apparent molar volumes. The polymer contents have the largest effect on increasing the compressive strength of cement paste, followed by the w/c ratio and curing time.

Mechanism study on the effect of diammonium hydrogen phosphate on the setting time and micro-nanostructure of ordinary Portland cement paste

The effect of diammonium hydrogen phosphate (DAP) on the setting time, mechanical properties and micro-nanostructure of cement paste is investigated. The results show that with an increase in DAP content, the peak value of hydration heat of cement is delayed, but the 3d cumulative hydration heat release of the cement is basically the same. The 3d compressive strength of cement paste is not significantly different, and the 28d compressive strength increases first and then decreases. When the DAP content is 0.5 wt%, the compressive strength of cement paste is most significantly improved, increasing by 38.5%. Meanwhile, the initial and final setting times of cement paste are extended by 74.0% and 73.2%, respectively. When the DAP content is 1.0 wt%, the cement paste has the longest setting time, with the initial and final setting times extended by 101.8% and 103.5%, respectively. However, the compressive strength of the cement paste can still be improved by 10.5%. It is mainly due to the change of pH value and calcium ion concentration of cement pore solution with different DAP content, which changes the micro-nanoscale morphology of C-S-H gel, Hamaker constant between globules, microscopic Young's modulus, and pore structure.

Valorization of Marble Waste Powder as a Replacement for Limestone in Clinker Production: Technical, Environmental and Economic Evaluation

This research combines technical, environmental, and economic aspects regarding the utilization of Bege Bahia marble waste (BB) in clinker production. Three different eco-friendly clinkers were produced, investigated, and compared with one that is commercially available. BB was used to replace 49.2%, 77%, and 80.3% of the limestone by total amount of clinker. Two clinkers were selected to produce cement pastes, and their impact on compressive strength at 28 days was examined. The results suggest that substituting limestone with BB does not adversely affect the compressive strength of cement paste. Moreover, employing 77% or 80.3% BB in clinker production does not significantly influence the alite and belite contents but slightly increases the tricalcium aluminate and ferrite phases while reducing the periclase content. A life cycle analysis was conducted to assess the effects of replacing limestone with marble waste. The results revealed a substantial decrease in abiotic depletion, leading to conservation of substantial natural resources. Consequently, the utilization of BB in clinker production makes a significant contribution to environmental preservation while providing an effective alternative to limestone. In addition, the resulting clinkers serve as useful repositories, providing a permanent and sustainable destination for waste that is currently deposited in landfills. Finally, the economic viability was also examined under various scenarios based on the distance between marble and cement plants. The results highlight the transport distance of marble waste as the primary determinant of economic feasibility in utilizing this residue as a limestone replacement.

Recycle of discarded masks in civil Engineering: Current status and future opportunities with silane coupling agent modified discarded masks

In recent years, with the heightened of public health protection awareness, masks have become an important protective equipment. The accumulation of discarded masks (DM) poses an impact to environment and resource. Recycling DM has become a prime focus of sustainable development research. This investigation introduces a review of the recycling of DM in civil engineering and presents a novel modification of discarded mask fibers (DMF) to enhance the mechanical property of cement paste. In the review section: (1) The masks are divided into three classes by integrating relevant standards and considering mask protective characteristics; (2) Various disposal techniques for recycling DM are categorized in shredding, hot processing, paper shredding, and crushing; (3) The impact of incorporating DMF in concrete, mortar, asphalt, road subbases and base courses are discussed. The enhancement of applying DMF into composite materials varies depending on the specific application. In the experimental research section, the silane coupling agent (SCA) is introduced as a modification to improve the weak bonding between DMF and composite materials. The SCA-modified polypropylene (PP) fibers were conducted as a control group. The results indicate that the compressive strength of cement paste with both SCA-modified DMF and PP fibers increased by 12.29 % and 26.10 %, respectively. Finally, several future opportunities in recycling of DM in Civil Engineering were drawn.

Effect of chelator on compressive strength and microstructure of CO2 curing cement paste

In this paper, chelator was used to accelerate CO2 mineralization curing cement paste. The mechanical properties and microstructure of CO2 curing cement paste with chelator were investigated through compressive strength test, low-field nuclear magnetic resonance (NMR) test, and scanning electron microscopy (SEM) observation. Next, the effect of chelator on the content of mineralized products was analyzed through X-Ray diffraction (XRD) test and thermogravimetric analysis (TGA). Finally, the CO2 absorption capacity of cement paste with chelator was evaluated through carbon sequestration rate calculation. The results showed that the chelator could improve the strength of CO2 curing cement paste and accelerate the mineralization reaction rate. With the increase of the chelator dosage, the compressive strength of cement paste presented a trend of first increasing and then decreasing. When the dosage of chelator was 0.5% of the cement content, the improvement effect on compressive strength of cement paste was the best, and under the premise of achieving equivalent mechanical properties, chelator could shorten the CO2 curing period of cement paste by half. NMR showed that chelator could promote the conversion of large pores to small pores in hardened cement paste. CO2 curing for 4 h, the porosity of pores above 40 nm in cement paste with 0.5% chelator decreased by 17.0% compared to ordinary cement paste. Based on the XRD and TGA on the mineralization reaction zone, it was found that the addition of 0.5% chelator could improve the CO2 curing degree of cement paste. CO2 curing for 48 h, the 0.5% chelator could effectively increase the yield of mineralized product CaCO3 by 22.5%. CO2 curing for 4 h and 48 h, the cement paste with 0.5% chelator could increase the carbon sequestration rate by 11.8% and 17.4% compared with ordinary cement paste, respectively.

Corrosion law of cement paste under hydrogen sulfide conditions in natural gas wells

Downhole anticorrosion in sour gas (H2S or CO2) wells is one of the technical problems in petroleum engineering, and the corrosion law of cement paste, which is the “first barrier of the wellbore,” needs to be focused on. Aiming at the problems existing in the current research on the corrosion of underground cement paste, a curing method for interfacial corrosion is proposed. X-ray diffraction and scanning electron microscopy are used to investigate the corrosion mechanism of cement paste cured under hydrogen sulfide (H2S) conditions in natural gas wells. Experimental results showed that the corrosion depth of cement paste is proportional to the partial pressure of H2S and the corrosion time, and the compressive strength of cement paste after corrosion is inversely proportional to the H2S partial pressure value and the corrosion time. Due to the gradual enrichment, accumulation, and migration of products after the cement paste is corroded by H2S, the cement paste forms a relatively stable dense layer or corrosion transition zone. The porosity and permeability of cement paste after corrosion increased with corrosion time, showing the characteristics of first increasing and then decreasing and finally making it more difficult for the corrosive medium to enter the interior of the cement paste. It is an important method stable corrosion transition zone forms as soon as possible, which is important to maintain the long-term sealing and chemical integrity of the cement sheaths in natural gas wells containing H2S.

Effects of recycled concrete powders on the rheology, setting and early age strength of cement paste

This work studies the effect of substitution rate and types of recycled concrete powders (RCPs) on the rheology over time, setting time, and 1 day compressive strength of cement paste. Two RCPs with distinct compositions, namely RCPI and RCPII, were adopted. Results showed that incorporating RCPs contributes to the hydration of cement paste in the first 5 h, and the initial zeta potential of cement paste is reduced after replacing cement by RCPs, which results in that utilizing RCPs increases the initial rheological properties of cement paste and its growth rate over time. Specifically, the paste with 30% RCPs exhibits 66.85–122.79% higher initial static yield stress than the pure cement paste, and the structuration rate in the paste with 30% RCPs is 10.26–141.03% higher than that of plain paste. Utilizing RCPs decreases the initial setting time. Utilizing RCPs is detrimental to the hydration reaction beyond about 8 h and pore structure of cement paste, the total porosity of paste with 30% RCPs at 24 h is 11.31–13.70% higher than that of plain paste, and the content of harmful and more harmful pores shows an increase of 19.30–30.43%, which results in a nearly 50% reduction in the 1 day compressive strength. Compared to the RCPI cement paste, the RCPII cement paste with the same RCP content exhibits lower initial rheology, higher growth rate of rheological parameters, lower total porosity, thus has relatively higher 1 day compressive strength.

A new enhanced carbonation curing method using monoethanolamine (MEA) solution: Their effects on hydration and microstructure of cement-based materials

CO2 curing can improve the properties of cement-based materials and absorb the CO2, which is an effective method for pre-cast concrete. However, the application of CO2 curing is limited for the on-site concrete because the CO2 is hard to diffuse into inner fresh concrete. A new enhanced carbonation curing method has been proposed by using monoethanolamine (MEA) solution in this study. In addition, the effect of new carbonation curing on the compressive strength, hydration and microstructure has been studied. The results showed that the MEA solution can delay the hydration of cement which affects the pore structure and reduce the compressive strength. The effect of CO2-rich MEA solution on the compressive strength of cement paste is quite different from that of MEA solution. The inhibition effect of CO2-rich MEA solution that absorbs carbon dioxide on the early hydration of cement is weak, and the promotion effect on the later hydration is more obvious. The CO2-rich MEA solution can chemically react with the calcium ions in the cement slurry pore solution to generate calcium carbonate, and the small amount of calcium carbonate generated can promote the later hydration of cement.

A study of the association involving pore characteristics and compressive strength of cement pastes incorporating fine fly ash

The evaluation of mechanical properties in materials derived from cements incorporating ultrafine fly ash was performed. An examination of the influences of curing time, fly ash concentration, and particle size on the compressive strength of materials derived from cements was executed. Upon the integration of ultrafine fly ash into materials derived from cements, the pore structure was scrutinized using the mercury intrusion technique, and the impact of fly ash concentration and particle size on diverse pore structure parameters was investigated. According to the findings, the quantity of macropores in materials derived from cements progressively diminished with the rise in fly ash concentration, and the porosity consistently decreased with the extension of curing time, culminating in an elevation of compressive strength. The proportion of gel pores in materials derived from cements contracted with the increment in fly ash concentration, resulting in a decline in compressive strength. Fly ash particles of reduced dimensions exhibit heightened compressive strength due to the diminution in particle size. Employing fractal theory, the fractal dimension of the pore surface in materials derived from cements was ascertained, and an outstanding correlation between the fractal dimension and the total pore surface area was discovered. Grounded in the connection concerning the compressive strength of materials derived from cements and assorted pore structure parameters, a suitable relationship model has been devised between the total pore volume, transitional pore volume, and compressive strength. At the same time, a fitting scope of the model had been determined.