Compressive Strength Development Research Articles

Assessing the Influence of Calcium-Based Alkaline Activators and Metakaolin on the Compressive Strength Development of Geopolymer Concrete for Different Mix Design Parameters

Assessing the Influence of Calcium-Based Alkaline Activators and Metakaolin on the Compressive Strength Development of Geopolymer Concrete for Different Mix Design Parameters

Preparation of C-S-H seeds from waste glass powder and its effect on early performance of cement paste

This study investigates the hydrothermal synthesis of calcium silicate hydrate (C-S-H) seeds using nano-size glass powder (NGP) derived from siliceous raw materials and CaO as the calcareous precursor. The influence of varying NGP concentrations on the particle size, microstructure, and phase composition of the C-S-H seeds was systematically analyzed. The synthesized C-S-H seeds were subsequently employed as additives to evaluate their effects on the early hydration process and compressive strength development of cement paste. The results indicate that increasing the NGP concentration from 0.2 mol/L to 0.8 mol/L leads to an exponential increase in the median particle size of the C-S-H seeds from 147 nm to 1328 nm and a corresponding morphological transformation from flocculent to granular structures. Additionally, the purity of the C-S-H sample decreased from 74.8% to 54.5% as the NGP concentration increased. The addition of C-S-H seeds can increase the 12h compressive strength of cement pastes by 15.5%–53.5%. This improvement is due to the accelerated early hydration kinetics induced by the C-S-H seeds, which act as nucleation sites, thereby increasing the nucleation and growth rates by 31.4% and 53.2%, respectively.

ITZ properties of LWA surroundings in high strength mortar according to LWA/sand with relative humidity

The internal moisture content significantly influences the quality and durability of cement-based composite materials. However, reliable methods to analyze the moisture retention of concrete and mortar are lacking, particularly in relation to internal curing with lightweight aggregates (LWA). In this study, the internal moisture retention of mortar with different lightweight aggregate/sand (L/S) ratios was investigated while considering the absorption characteristics of LWA. Furthermore, the impact of internal moisture retention on the development of the interface transition zone (ITZ) between the LWA and cement matrix was analyzed. Additionally, compressive strength development was evaluated over different curing periods (3, 7, 28, 56, and 90 days) under internal curing conditions. The results showed that the L/S ratio, which is directly proportional to the amount of moisture absorbed, enhanced the compressive strength and plastic hardness, contributing to the development of depletion of internal moisture in the mortar was could be observed. The moisture consumption for different types of LWA was analyzed using CT scanning. XRD and SEM-EDS analyses confirmed the abundant presence of hydration products in the ITZ. This study demonstrates that the L/S ratio that considers the LWA absorption characteristics, can serve as a critical parameter for precisely correlating the curing time and compressive strength in internally cured mortars.

Experimental studies for evaluation of the removal time of form on concrete using ultrasonic pulse velocity methods

In this study, the form removal time of concrete was evaluated using ultrasonic pulse velocity (UPV). The evaluation was performed based on the form removal strength specified in the American Concrete Institute (ACI), British Standard (BS), and Korean Construction Standards (KCS). Additionally, physical and mechanical properties of the concrete were evaluated from the early stages up to 28 days after casting. Specimens of both plain and lightweight concrete (LWC) were prepared for analysis. For the purpose of evaluating the concrete at various strengths, the water-to-cement (W/C) ratios were established at 0.41 and 0.28, aimed at achieving target compressive strengths of 30 MPa and 60 MPa for plain concrete, respectively. The measurement of mechanical properties was conducted through the assessment of penetration resistance, compressive strength, and ultrasonic pulse velocity (UPV). Models for predicting the strength based on regression analysis were proposed, taking into account the characteristics of the setting times (both initial and final). Additionally, the aggregate cross-section, matrix structure, and crystalline phases were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). In the results of the experiments, it was observed that Mortar60 reached both initial and final set quicker than Mortar30, a phenomenon attributed to the higher cement content. Initially, Plain and LWC specimens exhibited comparable trends in compressive strength and ultrasonic pulse velocity (UPV). However, when examining the compressive strength development from 1 to 28 days, a notable difference of approximately 33 % was observed between Plain60 and LWC60. Similarly, differences in UPV ranged from 10.12 % to 11.88 %. The logistic regression model was found to predict the form removal strength more accurately than the exponential model, as indicated by the regression analysis results. When these results were compared with previous strength prediction models, the difficulty in predicting form removal strength became evident, primarily due to the substantial errors present in these models. Analysis using scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed the presence of hydration products within the lightweight aggregate, which signifies the hydration reaction. These products seemed to enhance the performance of the interfacial transition zone (ITZ) between the aggregate and cement paste. Furthermore, Mortar60 was characterized by larger crystalline hydration products, a denser matrix structure, and higher XRD peaks in comparison to Mortar30.

Strength, durability, and heat development characteristics of high-performance concrete containing ground coal bottom ash with low and high calcium

Currently, the availability of fly ash has reduced continuously due to the shutdowns of coal-fired power generating plant as climate change concerns have increased. Therefore, the aim of this paper is to find an alternative pozzolan by examining the employment of low- and high-calcium oxide (CaO) ground bottom ash which has been abandoned rather using in concrete production. The bottom ashes were blended with fly ash as a partial substitution of cement (OPC) by observing their generic effects on the compressive strength, cumulative heat generation, chloride ion penetration, and water sorptivity of high-performance concrete. The samples of bottom ash were prepared by oven drying, particle size cutting, and grinding to enhance the reactivity and consistency. High-performance concretes were made at a water-to-binder (W/B) ratio of 0.27 and partial replacement of OPC up to 50 % by weight of the binder. The results indicated that the concretes with 28-day compressive strengths of 101.0 and 109.0 MPa (21.6 % and 28.2 % stronger than OPC concrete) were produced with 50 wt% OPC replacement with high- and low-calcium ground coal bottom ashes (HCBA and LCBA), respectively. These findings suggest that HCBA and LCBA have high pozzolanic reactivity and high possibility for utilization as pozzolan or supplementary cementitious materials in concrete. In addition, the binary blended binders (OPC-HCBA and OPC-LCBA) and ternary blended binders (OPC-HCBA-FA and OPC-LCBA-FA) produced had better chloride ion penetration resistance, less cumulative heat evolution, and lower water sorptivity than 100 % OPC as a cementitious material. Partial OPC replacement by HCBA and LCBA improved the chloride ion penetrability class of OPC concrete from “very low” to “negligible.” The cumulative heat generation due to the pozzolanic reaction of HCBA and LCBA from the partial replacement of OPC up to 50 % reduced 30–44 % relative to the OPC-based mixture throughout during 72 hours after mixing. The CaO content strongly influenced early compressive strength development and cumulative heat evolution but had less impact on chloride ion penetration resistance and water sorptivity.

Optimization of Proportions of Alkali-Activated Slag-Fly Ash-Based Cemented Tailings Backfill and Its Strength Characteristics and Microstructure under Combined Action of Dry-Wet and Freeze-Thaw Cycles.

To enhance the application of alkali-activated materials in mine filling, cemented tailings backfill was prepared using slag, fly ash, sodium silicate, and NaOH as primary constituents. The effects of the raw material type and dosage on the backfill were examined through a single-factor experiment. Additionally, response surface methodology (RSM) was utilized to optimize the mixing ratios of the backfill, with a focus on fluidity and compressive strength as key objectives. The evolution of backfill quality and compressive strength under the combined effects of dry-wet and freeze-thaw (DW-FT) cycles was analyzed. The hydration products, microstructure, and pore characteristics of the specimens were analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and nitrogen adsorption tests (NATs) across varying cycles. The results demonstrate that the optimal backfill composition includes 47.8% fly ash, 6.10% alkali equivalent, and a 1.44 sodium silicate modulus. The macroscopic behavior of the backfill under DW-FT coupling followed this progression: pore initiation → pore expansion → crack formation → crack propagation → structural damage. After a minor initial increase, the backfill strength steadily decreased. Microscopic analysis revealed that the decline in internal cementation products and the deterioration of pore structure were the primary causes of this strength reduction. Thus, the DW-FT coupling can cause significant erosion of the backfill. The technical solutions presented in this paper offer a reference for solid waste utilization and provide valuable insights into the durability of backfill under DW-FT coupling.

Effect of different amounts of barium substitution for calcium on the hydraulic activity of the high belite binary C2S-C4A3$ system

The substitution of Ba2+ for Ca2+ in both dicalcium silicate (C2S) and ye'elimite (C4A3$) has the potential to stimulate the development of early hydration activity of high belite sulfoaluminate cement (HBSAC). To relieve the emission pressure of CO2 in the cement industry and promote the early compressive strength development of HBSAC, the C2S-C4A3$ binary system with different amounts of Ba2+ substitution for Ca2+ was synthesized and investigated in this study. The SEM-EDS and XRD test methods confirmed the stoichiometric composition of Ba-bearing C2S-C4A3$ binary systems. The results showed that Ba2+ tends to preferentially replace Ca2+ in C4A3$ compared to replacing Ca2+ in C2S, resulting in more substitution amount of Ba2+ in C4A3$ mineral, as the designed substitution amount of barium increased from 25 wt.% to 55 wt.%, the stoichiometric formula of Ba-bearing C2S was transformed from Ca1.66Ba0.34SiO4 to Ca1.45Ba0.55SiO4, and the stoichiometric formula of Ba-bearing C4A3$ was transformed from Ca2.29Ba1.71Al6SO16 to Ca0.86Ba3.14Al6SO16. While excessive amount of barium (more than 45 wt.%) resulted in the increased content of by-products, such as BaSO4 and BaAl2O4, as well as the formation of C3S. The hydration properties of each group of synthetic clinker were investigated, including compressive strength, qualitative and quantitative analyses of the hydration products, leaching solution environment, and micromorphological analysis. The hydration products including C-(A)-S-H and AH3, as well as hydroxide (Ca(OH)2 and Ba(OH)2·8H2O), which can be carbonated to form carbonates (BaCO3 and CaCO3) by CO2 in the air. As the substitution amount of Ba2+ increased from 25 wt. % to 35 wt. %, the hydration degree of Ba-bearing α′L-C2S was promoted in the early stage, and the presence of C3S may affected the increase of early hydration activity of Ba-bearing α′L-C2S, however, the hydration degree of α′L-C2S with the most amount doping of barium in A055 samples exhibited the highest hydration degree of 88.0 % after hydration for 90 days. The compressive strength of high belite C2S-C4A3$ binary system of 3-day displayed a rapid increase from 8.6 MPa to 16.1 MPa, with the amount of barium increased from 25 wt. % to 55 wt. %. The compressive strength of A025 and A035 after hydration for 90 days increased steadily, reaching 35.0 MPa and 34.0 MPa respectively. However, the compressive strength of hydrated A045 and A055 samples for 90 days deteriorated and even cracked seriously for the hydrated A055 sample, which was attributed to the formation of a large amount of Ba(OH)2·8H2O and BaCO3 by excessive barium amount, and leading to the expansion and broken of the matrix. Thus, the designed amount of barium substitution for calcium in the C2S-C4A3$ binary system should be controlled, for a higher content of barium more than 35 wt. % could be damage to the development of the long-term hydration strength of the clinker. These results provided a theoretical basis to make it possible for the large-scale application of activated HBSAC, devoted to the sustainable development of infrastructure.

Evaluation of the Na-EDTMP/borax system as a non-dispersing, high temperature retarder for oil well cement

For well cementing at temperatures above 120 °C, thermal thinning depicts a major problem, promoting particle sedimentation via decreasing slurry viscosities. This is partly caused by dispersing properties of common high temperature retarder systems and can lead to imperfect zonal isolation, endangering the stability of the wellbore. Counteracting additives tend to start losing their effectiveness at temperatures >140 °C. Other options are often not economically sufficient, increase system complexity or show negative interactions with other additives.Hence, this work presents a comprehensive study on the sodium ethylenediamine tetra(methylene phosphonate) (Na-EDTMP)/borax retarder system, which was found to combine sufficient retardation with low thermal thinning, leading to an enhanced slurry stability at high temperatures. Thickening times (TT's) from 7 to 13 h (increasing with temperature) were achieved from atmospheric pressure and 50 °C up to high pressures and temperatures (HP/HT) of 19.0 kpsi and 200 °C bottom hole circulating temperature (BHCT). Furthermore, On/off-cycle HP/HT consistometer tests at 160 and 190 °C and rheological measurements were performed to examine stability of the slurry's viscosity. Experiments with fluid-loss additives show potential compatibility with other additives.Total retarder dosages of 0.97–2.64 % bwoc (by weight of cement) were applied. Compared to prior literature, higher Na-EDTMP/borax ratios (0.29–0.34 vs. 0.055) were found to improve retarding performance probably by enhancing synergetic effects. The slurries featured a sufficient initial viscosity (<40 Bc) and a constant pumpability (10–25 Bc) during the tests followed by a swift setting and compressive strength (CS) development. Additionally, high slurry stability was shown and compatibility with common fluid-loss additives is probable. Main disadvantage was the relatively high sensitivity of the system, especially at moderate temperatures, requiring exact dosage.Summarizing, the Na-EDTMP/borax retarder system might present a low-complexity opportunity for common high temperature retarders, avoiding thermal thinning while improving slurry stability.

Internal hydrophobic treatment for mortar containing supplementary cementitious materials: thermal analysis of kinetics and products of hydration

AbstractThe presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped.

Research on the strength influence and crack evolution law of layered backfill based on macro and meso mechanical response

This article analyzes the effects of inclined angle (IA), filling times (FTs) and cement tailings ratio (CTR) on the uniaxial compressive strength (UCS) and crack development law of layered cemented backfill (LCB) using various research methods, including indoor experiments, numerical simulation, and computed tomography (CT) scanning. The research shows: (1) In the indoor experiments, it was observed that increasing the IA, increasing the number of FTs, and decreasing the CTR had a significant weakening effect on the UCS of the specimens. The greater the IA, the more pronounced the separation and dislocation of the layered contact surface, resulting in a significant increase in macroscopic cracks at the bottom. As the FTs increases, the center of gravity of the failure of the LCB gradually moves downwards. This causes the damage and failure time to advance, and the peak stress to change from one main crack to multiple main cracks. (2) During the numerical simulation, compressive stress accumulates and increases around the pores in the layered contact surface. Microcrack aggregation occurs on the contact surface, and downward expansion and extension. The peak strain energy decreases as the IA increases with the FTs. The number of shear cracks increased more at 20° to 30° than at 0° to 20°. The strain energy of the 0° specimen is the highest, while that of the 30° specimen is the lowest. (3) The CT scan shows that the LCB is affected by stress conduction hysteresis. When the bottom backfill is in the stage of crack evolution, the top backfill is in the stage of compaction.When the LCB reaches the peak stress, both the bottom and middle layers of the backfill lose load-bearing capacity, and the top layer of the backfill has no cracks. This paper provides reference value and research ideas for the destruction of backfill that contain layered defective structures.

Apparent Influence of Anhydrite in High-Calcium Fly Ash on Compressive Strength of Concrete

This case study investigates five fly ashes with high CaO and SO3 levels in their chemical composition and compares the apparent influence of the presence and absence of anhydrite on compressive strength. Another distinguishing feature of the above ashes is that they, more or less, naturally contain anhydrite. Two different series of mixed proportions were adopted. Series 1 is designed to understand the maximum possible replacement level of fly ash. Series 2 is designed to understand the effect of anhydrite on compressive strength development. The mineral composition and glass phase of fly ashes were determined by X-ray diffraction Rietveld analysis. As a result of this study, we have found that concrete containing anhydrite-rich fly ash exhibits a higher strength than concrete containing anhydrite-free fly ash at all ages. The compressive strength increases with an increasing fly ash replacement ratio when anhydrite-rich ash is used, but strength decreases when the replacement level exceeds a certain point. The optimal amount of anhydrite was 2 ± 0.5 kg/m3 of concrete, excluding the anhydrite contained in cement.

The use of graphene nanoplatelets for enhancement of the compressive strength of mortar containing high-levels of natural Pozzolan

High Pozzolan concrete has an extended setting time and inhibits early-age compressive strength development, which can cause construction delays and limit its application in the concrete industry. The main aim of this study is to evaluate the effectiveness of graphene nanoplatelets (GNPs) in enhancing the mechanical properties of mortar containing high levels of natural Pozzolan. In the beginning, a relatively simple ultrasonication treatment process produced an almost uniform dispersion of GNPs in the mixing water to avoid agglomeration which limits the efficiency of GNPs. Tests on engineering properties indicated that the compressive strength of mortar containing 40 and 60 % natural Pozzolan as a partial replacement of cement was enhanced with the addition of the optimum content of graphene nanoplatelets which was found to be 0.03 % and 0.01 % by weight of binder at 40 % and 60 % cement replacement levels, respectively. The compressive strength was enhanced by 29.6 %, 27.4 %, and 27.5 % at 40 % cement replacement level, and by 86.3 %, 23.7 %, and 25.8 % at 60 % cement replacement level at 7, 28, and 56 days of curing, respectively. SEM investigations indicated that the addition of GNPs densified the structure thus enhancing the performance of mortar.

The utilization of pulverized waste tire rubber in a soil–cement composite for sustainable compressed earth brick production

This study examined the suitability of blending waste tires with cement in indigenous soil for producing compressed earth bricks (CEB) to achieve a sustainable environment. CEB was produced with clay soil and a combination of cement at 5 and 10% levels with varying dosages of pulverized waste tire at 0, 2.5, 5, 7.5, and 10% mixture. Classification tests were conducted to determine engineering properties such as the particle size distribution, Atterberg limit, specific gravity, optimum moisture and unit weight of the soil. The physical properties of the pulverized tire were evaluated. Moreover, density, water absorption, and compressive strength were determined for hardened CEB samples produced from mixtures of soil and various proportions of blended cement and pulverized waste tire materials. The classification results showed that the soil was silty clay of low plasticity. The density of the CEB samples was observed to increase slightly with the addition of blended cement-tire residue. Furthermore, a considerable improvement in the compressive strength development of the CEB was observed; however, compared with those of the control, the peak compressive strength of the CEB samples was greater when the soil was stabilized with 7.5% pulverized waste tire material and 10% cement. A decrease in the water absorption capacity of CEB was observed with an increase in the amount of pulverized waste tire and cement in the soil mixture. The response models corroborate the experimental findings indicating that amount of waste tire rubber residue and cement had significant effects on the CEB performance. This study ensure the beneficial recycling of waste tires blended with cement in soil for making medium-strength CEB to achieve sustainable, resilient masonry construction applications.Graphical

Phase evolution and microstructure changes induced by accelerated carbonation in natural hydraulic lime paste with GGBFS addition

Carbonation is a primary factor driving the continuous improvement of the long-term performance of natural hydraulic lime (NHL). This research systematically examines the impact of accelerated carbonation (3 % CO2) on the carbonation depth, phase composition, microstructure, and compressive strength of hardened natural hydraulic lime (NHL) pastes mixed with different amounts of ground granulated blast furnace slag (GGBFS), termed as S-NHL. The findings show that the hydration reaction products of GGBFS and Ca(OH)2 (CH), such as C3AH10, C4AĈH11, and C-S-H, densify the microstructure of S-NHL, resulting in a decrease in carbonation depth with increasing GGBFS content. Accelerated carbonation (AC) promotes the rapid transformation of a significant quantity of CH into calcite in S-NHL, with the carbonation of CH occurring more readily than the carbonation of hydration reaction products. Throughout the AC process, NHL contains only calcite-type calcium carbonate. In contrast, after 28 days of AC, the carbonation of hydration reaction products such as C3AH10 and C-S-H in S-NHL produces a minor amount of aragonite and vaterite. AC continuously reduces the total pore volume and porosity of S-NHL, but the average pore diameter and most probable pore diameter initially decrease and then slightly increase. AC significantly reduces the large pores in S-NHL, ultimately resulting in pores predominantly composed of capillary pores (50–1000 nm). AC facilitates the development of compressive strength in S-NHL paste, with the increase in compressive strength being positively correlated with its CH content.

A Prediction Model for the Unconfined Compressive Strength of Pervious Concrete Based on Mix Design and Compaction Energy Variables Using the Response Surface Methodology

Pervious concrete is desirable for water drainage in building systems, but achieving both high strength and good permeability can be challenging. Also, the importance of compaction energy is significant in determining the efficiency of pervious concrete. However, research on the development of unconfined compressive strength (UCS) prediction models for pervious concrete materials that incorporate compaction energy parameters remains unexplored. Therefore, this study aimed to balance strength and permeability while optimizing the compaction energy required for concrete production. A Central Composite Design (CCD) was used to design experiments within the response surface methodology (RSM) and evaluate the UCS, the porosity and permeability of pervious concrete specimens produced with varying cement content (280.00–340.00 kg/m3), the water-to-cement ratio (0.27–0.33), the aggregate-to-cement ratio (4:1–4.5:1), and compaction energy (represented by VeBe compaction time, 13–82 s). A regression model with goodness of fit (R2adjusted &gt; 0.87) was calibrated to estimate the UCS of pervious concrete as a function of mix design parameters and VeBe compaction time (Tvc). This model can potentially guide field practices by recommending compaction strategies and mix designs for pervious concrete, achieving a desirable balance between mechanical strength and hydraulic permeability for building construction applications.

Analysis of the Impact of Superplasticizer on the Compressive Strength of Periwinkle Shell Concrete

This research project investigates the compressive strength characteristics of superplasticized concrete incorporating periwinkle shell (PS) as partial replacements for granite coarse aggregate. The study aims to assess the influence of superplasticizer content and curing age on the compressive strength development of the novel concrete mixtures. Comparative analysis with plain concrete (control specimen) reveals that superplasticized concrete with periwinkle shell partial replacement exhibits a slower strength development. Results indicate that the compressive strength of superplasticized PS concrete attains its maximum strength (22.07 kN/mm²) at 21 days with a 15% partial replacement and 0.5% superplasticizer content. The findings suggest that optimal strength development for PS partial replacement performs best at higher percentages (15%). Concerning the workability of fresh concrete, PS partial replacement exhibits a consistent increase in slump values with higher percentages of replacement and superplasticizer content, peaking at 55mm at 15% partial replacement and 1.5% superplasticizer content. This study contributes valuable insights into the optimization of compressive strength and workability of superplasticized concrete with PS partial replacements, offering a sustainable and resource-efficient alternative to conventional concrete mixtures

Nanocrystalline Cellulose to Reduce Superplasticizer Demand in 3D Printing of Cementitious Materials.

One challenge for 3D printing is that the mortar must flow easily through the printer nozzle, and after printing, it must develop compressive strength fast and high enough to support the layers on it. This requires an exact and difficult control of the superplasticizer (SP) dosing. Nanocrystalline cellulose (CNC) has gained significant interest as a rheological modifier of mortar by interacting with the various cement components. This research studied the potential of nanocrystalline cellulose (CNC) as a mortar aid for 3D printing and its interactions with SPs. Interactions of a CNC and SP with cement suspensions were investigated by means of monitoring the effect on cement dispersion (by monitoring the particle chord length distributions in real time) and their impact on mortar mechanical properties. Although cement dispersion was increased by both CNC and SP, only CNC prevented cement agglomeration when shearing was reduced. Furthermore, combining SP and CNC led to faster development of compressive strength and increased compressive strength up to 30% compared to mortar that had undergone a one-day curing process.

Low-calcium CO2 sequestration materials prepared with full-component solid waste based on lithium slag as crystal regulator

High performance low calcium CO2 sequestration materials (LCCSM) were prepared by using carbide slag (CS), copper tailings (CT) as main raw materials and lithium slag (LS) as crystal regulator at 1260 °C for 1 h. The effects of lithium slag content on the crystal transformation and carbonation hardening behavior of low calcium CO2 sequestration material (LCCSM) were studied. The results show that with the increase of LS content (i.e. from 0 % to 3 %), the C3S2 content was increased continuously, and the sum of C2S (i.e., β-C2S and γ-C2S) content was decreased continuously. Due to the activity energy of β-C2S was lowest in first stage carbonation, which accelerates carbonation reaction of the overall LCCSM clinkers and releasing a large amount of heat. Thereafter, the hydration reaction of β-C2S was accelerated significantly and the hydration products will be further carbonated. The minor LS (i.e., 1 %) significantly improved the carbonation activity of LCCSM clinker. Thus, the compressive strength development and degree of carbonation of carbonated compact made by LS-1% was obviously enhanced than that of other LCCSM clinker during the first 24 h. This finding could provide guidance for the obtaining high performance low-calcium CO2 sequestration material based on multiple solid wastes. And also proposed a new perspective for the mechanism among the multi-phase coexistence, crystal transformation and their synergistic carbonation sequestration of calcium silicate clinkers.

Effect of steam curing system on compressive strength of recycled aggregate concrete

Abstract Steam curing prefabrication is a feasible way to promote the application of recycled aggregate in the background of building industrialization. The combined use of slag and fly ash contributes to the comprehensive improvement of both the early and later-stage performance of recycled aggregate concrete (RAC). However, the steam curing regime for RAC composed of slag and fly ash remains unclear, including appropriate curing temperatures and time. In this study, the influences of curing temperatures (20, 40, 60, and 80°C), steam curing time (6, 9, and 12 h) and mineral admixtures (slag powder and fly ash) on the demoulding strength and strength development of RAC were investigated. Based on the Arrhenius formula, the hydration reaction rate was characterized by the development of compressive strength, the apparent activation energy related to the steam curing time was calculated, and the energy-based compressive strength model was proposed to realize the early strength prediction of the steam-cured RAC.

The Contribution of Nano-Alumina to Ultra-High-Performance Cement-Based Systems.

In the last decades, nano-silica (NS), nano-alumina (NA), and nano-calcium oxide (NC) particles have been incorporated into cementitious materials, and it seems that each one of them contributes uniquely to the materials' properties. This research explores the influence of each nanomaterial on the fresh properties of cement pastes and their compressive strength evolution over one year. Low proportions (1.5% by weight) of nanomaterials were added to cement pastes, and their fresh properties, such as heat of hydration and X-ray diffraction patterns in the first hours, were analyzed. The compressive strength and open porosity were also measured long-term. The acceleration of hydration heat in NA-cement pastes is linked to enhanced hydration product formation at early ages. Among the tested nanomaterials, NA increased compressive strength by 10% at later ages. Although the fresh properties of NC-cement pastes remained unaffected, their open porosity decreased by 54% at 28 days. In contrast, the increase in heat of hydration in NS-cement pastes did not result in significant strength improvement. Based on these findings, NA was selected for ultra-high-performance cement (UHPC)-based material use. Its incorporation not only preserved the ultra-high-performance (UHP) properties but also provided additional benefits such as an increase in compressive strength under a CO2 atmosphere. Through detailed analysis, this research establishes that nano-alumina incorporation optimizes the microstructural development and compressive strength of ultra-high-performance cement-based systems, presenting a novel advancement in enhancing the mechanical properties and durability of these materials under various environmental conditions.