Early Strength Research Articles

Mechanical and microstructural characterization of one-part binder incorporated with alkali-thermal activated red mud

The traditional production of silicate cement is associated with substantial carbon emissions and environmental degradation. In contrast, cementless alkali-activated binders, derived from solid waste and industrial byproducts, have garnered significant interest for their reduced material costs, energy efficiency, and environmental benefits. This research investigates the application potential of an advanced mixture of anhydrous sodium silicate and red mud in one-part alkali-activated binders. It is assessed through various analytical techniques, including compressive strength, X-ray diffraction, fourier transform infrared, thermogravimetric analysis, digital image correlation, and scanning electron microscopy with energy dispersive spectroscopy. Findings demonstrate that the synergy between red mud and anhydrous sodium silicate markedly enhances the early strength of one-part alkali-activated binders incorporated with alkali-thermal activation. The increment in sodium silicate content is pivotal for bolstering binder performance. A 40 % red mud admixture results in a compressive strength of 40 MPa, achieving an optimal carbon-to-strength ratio. The inclusion of polypropylene fiber significantly influences the mode of compression failure in alkali-activated binders. Alkali-thermal activation of red mud elevates the levels of active silicon and aluminum, markedly augmenting the reactive silica and aluminum content. This modification fosters the disintegration and reorganization of Si-O and Al-O bonds in silica-aluminum materials, culminating in a denser structure. This structure is characterized by the generation of amorphous ((N, C)-A-S-H) gels, contributing to the material's enhanced properties.

Enhancing Concrete with Ultrafine Fly Ash: Mechanical Strength and Frost Resistance

Fly ash, a byproduct collected from the flue gas of coal combustion, serves as an effective additive in concrete. It offers environmental benefits by converting waste into a valuable resource, thus promoting energy conservation, emission reduction, and waste utilization. Additionally, fly ash enhances the mechanical properties and frost durability of concrete. Commonly used as a partial substitute for cement, it helps conserve resources. However, its use may compromise early strength and durability, which limits its applications. The transformation of raw fly ash into ultrafine fly ash through mechanical grinding increases its fineness and specific surface area, thereby boosting its reactivity and micro-aggregate effects. This process produces denser C-S-H gel and optimizes the concrete microstructure. Research shows that although ultrafine fly ash may slightly reduce early concrete strength, it significantly enhances long-term strength, with a 10% substitution improving early compressive strength by 20.2% and later strength by 13.7%. However, excessive fly ash content can reduce frost resistance, with an optimal substitution level at 25% significantly enhancing this property compared to standard concrete. Blending ultrafine fly ash with other mineral admixtures further boosts mechanical properties and frost durability. Challenges include increased processing costs and early strength deficiencies, along with the necessity to control heavy metal content for environmental and health safety. Future research should aim to optimize fly ash particle distribution and reactivity, develop cost-effective production methods, and blend fly ash with other minerals to improve concrete’s mechanical and frost resistance properties, thus expanding its potential applications.

Early Age Strength of Development Ultra High-Performance Concrete Using Class-F Fly Ash and Local Materials for Repair

Early Age Strength of Development Ultra High-Performance Concrete Using Class-F Fly Ash and Local Materials for Repair

Experimental Study on the Effects of Tapioca Starch on Cement Mortar Quality Improvement.

In this study, the effect of tapioca starch (TP) on mortar was evaluated by incorporating TP into the mortar mixture. The evaluation involved analyzing the mortar's quality characteristics, performance, and fundamental quality improvements. The addition of TP resulted in a decrease in flow, which was attributed to increased viscosity. Specifically, a 10% reduction in flow was observed with a 0.025% increase in TP content. After 28 days, the impact of TP on the compressive strength of the mortar remained consistent, regardless of the TP amount. However, within the first 3 days, higher TP content accelerated strength development, with early compressive strength increasing by up to 20% at a 0.050% TP level. Additionally, bond strength improved by approximately 60% at a 0.050% TP concentration, and final shrinkage was reduced by 5%.

Carbonated calcium silicates as pozzolanic supplementary cementitious materials

This study examined the carbonation mechanisms and products of various precursors, including hydrated cement pastes and calcium silicate clinkers. Regardless of the materials investigated, all exhibited rapid carbonation reactions and achieved high degrees of carbonation. Calcium carbonate and siliceous gel were consistently formed as carbonation products. The starting materials significantly influenced the characteristics of the siliceous gel. Carbonated concrete pastes displayed a higher presence of alumina in the gel, resulting in greater surface area and nano-porosity compared to gels formed from calcium silicate clinkers. The pozzolanic reaction products also differed depending on the precursor, with carbonated concrete pastes forming C-S-H and AFm phases, while carbonated calcium silicate clinkers produced only C-S-H phase. Such variations impacted the evolution of mechanical performance in composite cements. Notably, carbonated composite cements containing recycled concrete pastes exhibited higher early compressive strength compared to carbonated calcium silicate clinkers. However, the final compressive strength is similar.

Influence of microwave curing on the early performance of heat-stored LC3 composites

Limestone calcined clay cement (LC3), as a new green cementitious material, has a wide range of functional applications in cement-based composite materials. Heat-stored LC3 effectively achieve energy-saving and carbon reduction in buildings. However, the addition of phase change material (PCM) particles leads to a significant decrease in strength, which imposes higher requirements on early performance. To address this issue, this study adopts microwave curing technology to rapidly enhance the early performance of heat-stored LC3, with a specific focus on the influence of microwave curing on the early mechanical properties, hydration products, and microstructure of heat-stored LC3. The results showed that microwave curing at a power of 320 W for 5 min increased the 3-day compressive strength of heat-stored LC3 by 87.3 %, without adversely affecting the later-stage strength, thus compensating for the deficiency in early strength. Microstructure and pore structure analysis revealed that the enhancement of early strength by microwave curing was mainly attributed to the promotion of early hydration of clinker and the activation of pozzolanic reaction occurred calcined clay. The additional formation of C-(A)-S-H gel reduced the matrix porosity, improved overall integrity, and enhanced the microstructure. Additionally, the temperature regulation capability of heat-stored LC3 was verified, ensuring its auxiliary temperature regulation function while maintaining reliable mechanical properties and excellent early strength.

Experimental Study on Performance and Mechanism of High-Strength Artificial Blocks Based on Dredged Silt

This paper investigates the preparation and properties of high-strength artificial blocks made from dredged silt with a clay content of 52.0%. A comparative analysis of the mechanical properties of dredged silt blocks produced using semi-dry pressing and vibration molding methods was conducted. The study examined the effects of using fly ash (FA) and ground granulated blast-furnace slag (GGBS) as substitutes for cement on the compressive strength, splitting tensile strength, and dry shrinkage of the blocks. Additionally, the microstructure of the dredged silt blocks was analyzed using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and thermogravimetric analysis. The results show that specimens prepared using the pressing method exhibit better mechanical performance with compressive and splitting tensile strength reaching 64.8 MPa and 5.6 MPa at 28 d, respectively, which increased by 111.07% and 143.48% compared to specimens prepared through vibration molding. The addition of FA and GGBS reduces the early strength of the block to a certain extent but without a significant adverse effect on later strength. GGBS demonstrates faster hydration and a better filling effect. The addition of GGBS or FA refines the pore structure and reduces the diameter of pores in the paste, which is beneficial for improving the dry shrinkage performance of the block. At 120 d, the dry shrinkage of blocks containing 50% FA and GGBS shows a reduction of 29.7% and 27.1%, respectively, compared to blocks made with cement. The properties of the silt blocks can be notably enhanced through mechanical force, particle gradation, and hydration action. The preparation of artificial blocks such as road bricks and ballast blocks using dredged soil as the main raw material has been applied in projects such as the Yangtze River waterway regulation in China and Skikda Port in Algeria.

Sustainable Ecological Non-Sintered Ceramsite (SENC) with Alkali Activators: Performance Regulation and Microstructure

The development of novel materials made from waste is one of the main measures to achieve sustainable materials development. In this study, ash of mushroom and corn straw (MCA) and furnace slag (FS) were used as raw materials to prepare alkali-activated biomass ash-slag material (AABS) and sustainable ecological non-sintered ceramsite (SENC). In this paper, the effects of quicklime powder (QL), NaOH, and sodium silicate solution (SS) on AABS were analyzed using single factor and orthogonal tests, and the preferred ratio of the composite alkali activator configuration was established. SENC was prepared based on the composite alkali activator, and the microstructure and phase composition of SENC were explored using XRD and SEM–EDS. The results showed that 3 wt% QL enhanced the early age compressive strength of AABS. The composite alkali activator was best configured when the additions of QL, NaOH, and SS were 3%, 2%, and 15%, respectively. At this configuration, the 28 d compressive strength of AABS was 47.4 MPa, and most of the internal pores were less than 0.4 μm; the 28 d numerical tube pressure of the SENC reached 12.2 MPa with a softening coefficient of 0.96. According to the results of XRD and SEM–EDS, SENC contained various hydration products such as C-A-S-H, calcium hemicarboaluminate, hydrotalcite, portlandite, and vaterite. The largest proportion of hydration products was C-A-S-H, which contributed to the pore refinement and structural densification. SENC has the potential to be used as coarse aggregate in sustainable lightweight concrete.

Enhancing carbonation resistance of calcium sulfoaluminate belite-based concrete: comparative analysis and admixing strategies

Calcium sulfoaluminate belite (CSAB)-based cement exhibits useful properties such as low CO2 footprint, high early-age strength and shrinkage compensating behavior. Our previous study examined the mechanism of carbonation in CSAB-based binder and reported a higher degree of carbonation in CSAB-based binder compared to Portland cement (PC) binder. This study examines the admixing strategies to improve the carbonation resistance of CSAB-based binders. The addition of gypsum or calcium hydroxide reduced the carbonation depth (in natural and accelerated environments) in the CSAB binder. Gypsum addition reduced the pH and resulted in pore refinement. Whereas calcium hydroxide addition increased the pH and promoted the formation of monosulfate (AFm). Although the carbonation depth was reduced in the presence of gypsum or calcium hydroxide, the addition of calcium hydroxide offered a better admixing strategy due to its higher pH which is crucial for the passivation of reinforcement.

Performance of high-strength green strain-hardening cementitious composites incorporating CSA/CAC cements and GGBS

Strain-hardening cementitious composites (SHCCs) possess crack control and durability properties. In the pursuit of reducing CO2 emissions and addressing potential issues of slow strength development for SHCCs with pozzolans, the objective of this study was to develop high-strength green SHCCs (HSG-SHCCs) that exhibit improved early strength, drying shrinkage, and environmental friendliness. A ternary binder system was proposed, comprising of ground granulated blast furnace slag (GGBS), ordinary Portland cement (OPC), and either calcium sulfoaluminate cement (CSA) or calcium aluminate cement (CAC). The fresh, mechanical, and durability properties of the proposed HSG-SHCCs were experimentally investigated. Additionally, the microstructures and chemical phases of the developed CSA/CAC-GGBS-OPC ternary binder system were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that the developed HSG-SHCCs demonstrated 6-hour and 28-day strengths of up to 11 MPa and 110 MPa, respectively. The CSA/CAC-based ternary binder system also exhibited enhanced durability and improved drying shrinkage. However, the inclusion of CSA and CAC in HSG-SHCCs could lead to a reduction in tensile performance, specifically in strain capacity. The main hydration products of the CSA/CAC-GGBS-OPC ternary binder system were C-S-H, ettringite, gibbsite, and calcium hydrate. In addition to the fresh, mechanical, and durability properties, the environmental impact of the developed HSG-SHCCs was also assessed. The results indicated that a 30 % replacement of OPC with CSA cement in the HSG-SHCC mix notably improved the trade-off among CO2 emissions, compressive strength, and tensile cracking resistance.

Influence of Nano-Activated CaCO3-Metakaolin on Early Strength and Microstructure of Cement

The early strength, microstructure, and structure of cement mortar under low-temperature curing conditions were investigated through compressive strength tests, scanning electron microscopy, x-ray diffraction, synchronous thermal analysis (thermogravimetric analysis coupled with differential scanning calorimetry), and nuclear magnetic resonance tests. The study focused on the impact of the single addition of nano-activated CaCO3 (NAC) and the simultaneous addition of metakaolin (MK) on cement mortar. The results indicate that the addition of NAC accelerated the early hydration of cement. At a 1% dosage, the compressive strength increased by 6.84%, 14.77%, and 18.58% at 1 day, 3 days, and 7 days, respectively. When 5% MK was co-added, the compressive strength increased by 15.16%, 27.85%, and 21.66% at 1 day, 3 days, and 7 days, respectively. The combination of NAC and MK accelerated the hydration of cement, refined the products, reduced the porosity, improved the microstructure, and enhanced the early compressive strength of cement-based materials.

Assessing Roller Compacted Concrete using GGBS as Partial Cement Replacing Material for Application in Low Traffic Volume Road

This paper reports most optimized mix derived from the roller compacted concrete (RCC) using ground granulated blast furnace slag (GGBS) as the partial cement replacing materials in the context of possible utilization of RCC in the construction of rigid pavements in the rural part of the country, especially subjected to low vehicular traffic volume. In the current study, various RCC mix compositions were developed by substituting ground granulated blast furnace slag (GGBS) for ordinary Portland cement (OPC) in varied percentages (0%, 20%, 40%, and 50%) and assessed for mechanical (strength) properties. All the three GGBS blended mix compositions are found to give early age compressive strength more than 20 MPa and 28 days compressive strength more than 30 MPa. Further, they are found to have split tensile strength in the range of 2.8-4.1 MPa. Moreover, they are found to yield the flexural strength more than 3.8 MPa. All the three mixes are found to comply with the requirements of compressive strength, splitting tensile strength and the flexural strengths as prescribed by Indian Roads Congress Specification and American Concrete Institute Standards for possible utilization in the construction of rigid pavements in the rural parts of the developing country like India. Further, the strength values of the GGBS blended mixes increases from 20% to 40% and decreases thereafter, at the higher GGBS contents such as 50%. In view of this, the RCC mix composition with 40% GGBS contents can be regarded as the most optimal mix to be used in the construction of rigid pavements in rural part of the country.

High temperature calcined red mud-cement mortar: Workability, mechanical properties, hydration mechanism, and microstructure

To efficiently utilize red mud (RM) in cement-based materials, this study employed high-temperature calcination to enhance RM's pozzolanic activity. Calcined RM replaced cement in RM-cement mortar, examining the effects of different calcination temperatures and RM addition amounts on the workability and mechanical properties of the mortar. Additionally, XRD, FTIR, SEM-EDS, TAM-Air, and TG were used to explore the hydration mechanism and microstructure of RM-cement mortar. Research showed that as the calcination temperature increased, minerals like Calcite, Hematite, and Cancrinite in RM began to decompose, and the glassy structure increased. At 800 °C, the serrated and amorphous diffraction peaks significantly increased. Calcined RM positively influenced the setting and hardening of cement mortar but negatively affected its fluidity. The optimal calcination temperature for RM was 800 °C, with an optimal addition amount of 10%. The compressive strengths of RM-cement mortar at 3, 7, and 28d, with optimal conditions, are 9.62, 29.94, and 40.12 MPa, respectively, showing increases of 4.25, 1.72, and 1.39 times over untreated RM-cement mortar. When RM was calcined to 800 °C, the diffraction peak intensities of Portlandite, C–S–H, and Ettringite in the RM-cement paste were the highest, and the hydration products interwove to form a dense microstructure. Adding calcined RM extended the induction period of cement, increased the rate of heat release, shortened the acceleration period, and further accelerated the rate of heat release. Nevertheless, the alkaline components in calcined RM pose a certain hindrance to the later stages of cement hydration. In summary, calcining RM to 800 °C enhanced its pozzolanic activity, improved the workability, early hydration, and early strength of cement, and reduced cement consumption and CO2 emissions.

Performance Evaluation and Mechanism Study of Solid Waste-Based Cementitious Materials for Solidifying Marine Soft Soil under Seawater Mixing and Erosion Action

The main purpose of this research is to develop a solid waste-based cementitious material (SWC) instead of cement for solidifying a large amount of marine soft soil with high water content and low bearing capacity in coastal areas. This aims to solve the problems encountered in the practical application of cement soil, such as slow strength growth and poor durability. The SWC includes ground granulated blast furnace slag (GGBS), dust ash (DA), and activated cinder powder (ACP), with admixtures of naphthalene sulfonate formaldehyde condensate (NS) and compound salt early strength agent (SA). Both the 7 d and 28 d compressive strength values of the SWC formulations G4 and G7 are about twice as strong as those of cement soil (GC), even when mixed with seawater. Immersion tests revealed that stabilized soil had superior resistance to seawater corrosion compared to cement soil. X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis explained that the main hydration products in cement soil are C-S-H and CH, while in stabilized soil, SWC generates a large amount of C-A-S-H with gelling properties and AFt with filling properties. These hydration products have better effects on strength and seawater erosion resistance.

The Research Effects of Variable Temperature and Early Strength Agent on the Mechanical Properties of Cement-Stabilized Macadam.

In cold regions with high daily temperature gradients (>20 °C), the durability of cement-stabilized macadam (CSM) base materials is poor and prone to cracking. To effectively reduce the cracking of semi-rigid base layers in cold regions with high daily temperature gradients and extend fatigue life, this study focused on cracking and fatigue characteristics of CSM with a 10% commercial early strength agent (ESA) added by the external mixing method under different curing conditions. The ESA was manufactured by Jiangsu Subote New Materials Co., Ltd. (Nanjing, China). The curing conditions were divided into variable temperature (0-20 °C) and standard temperature (20 °C). CSM curing was carried out through a programmable curing box. The research results indicated that the variable temperature curing conditions reduced the strength and fatigue resistance of CSM and accelerated the modulus attenuation rate of CSM. At the same time, the drying shrinkage of CSM was greater. The temperature shrinkage coefficient and strain of CSM under variable temperature conditions were smaller than those under standard temperature conditions. The effect of variable temperature conditions on the cracking and durability of CSM could not be ignored in cold regions. Compared to standard temperature curing conditions, the indirect tensile strength of CSM reduced by 31.04% under variable temperature conditions, the coefficient of variation increased by 2.97 times, and the discrete type significantly increased. Compared with CSM without ESA, the dry and temperature shrinkage strains of CSM with 10% ESA were reduced by 24.65% and 26.10%, respectively. At a stress level of 0.6, compared to standard temperature curing conditions, the fatigue life of CSM decreased by 97.19% under variable temperature conditions. Under variable temperature conditions, the fatigue life of CSM with 10% ESA increased by 196 times compared to 0% ESA. Adding ESA enhanced the anti-shrinkage cracking, strength, and durability of CSM under variable temperatures. ESA incorporation effectively compensated for the weakened characteristics of CSM under variable temperature conditions. The study proposed a practical approach for boosting the durability of CSM in cold environments.

Combined effect of supplementary cementitious materials and hot-dipped galvanized steel on performance of reinforced concretes subjected to chloride-induced corrosion

Concrete specimens with three types of cement (sulfate resistant high early strength – reference, pozzolanic, and with ground granulated blast furnace slag) reinforced with two types of steel (galvanized and carbon steel) were subjected to cycles of immersion in 1.0 M NaCl solution and drying at 40ºC. For each different steel-concrete condition, 6 rebars were tested. Experimental results show that galvanized steel presents longer corrosion initiation periods in concretes with supplementary cementitious materials. Particularly for pozzolanic concrete, this increased initiation period was 4.6 times longer on average, which reflects, in a similar way, on service-life simulations. In general, the average chloride thresholds of galvanized steel increased with a decrease in pore solution alkalinity. Compared to carbon steel, higher chloride thresholds were found for galvanized steel embedded in the lower alkalinity concrete matrix (calculated pore pH = 12.6). On the other hand, galvanized steel presented lower chloride thresholds for more alkaline pore pHs (pozzolanic and reference concretes).

A novel approach for high-efficient activation of large-volume slag cement towards a lower-carbon future in cement industry

Substituting ordinary Portland cement (OPC) with supplementary cementitious materials (SCMs) is a widely adopted strategy in the cement industry to reduce CO2 emissions. However, the low reactivity of SCMs often results in delayed early strength development when used in large quantities. This study aims to substitute 70 % of OPC with ground granulated blast furnace slag (GGBFS) and efficiently activate this system through calcium-ferrite-silicate-hydrates/polycarboxylate ether (C-F-S-H/PCE) nanocomposites and sodium sulfate. The findings indicate that the combined use of both activators has a significant positive effect on the strength development of this low-carbon cement, demonstrating comparable performance to OPC without any substitution. This can be attributed to the effective enhancement of the reactivity of the low-carbon cement, particularly GGBFS. Furthermore, the utilization of C-F-S-H/PCE nanocomposites improves the polymerization degree and leads to a more compact morphology of the calcium-aluminum-silicate-hydrates (C-A-S-H) gel without affecting the Al/Si. The proposed activation approach provides a foundation for the large-volume utilization of GGBFS and other SCMs in cement-based materials and holds enormous potential for reducing CO2 emissions in cement industry.

Development of 3D-printed magnesium silicate hydrate cement mixes involving metakaolin as a substitute for silica source

ABSTRACT The printability of MgO-SiO2 cement pastes involving the use of microsilica (MS) and metakaolin (MK) as a SiO2 source was thoroughly investigated. Fresh properties, including rheology and early-age strength, mechanical properties and microstructures of pastes incorporating different contents of MK were presented and analyzed. Amongst samples studied, those containing 5% MK as a substitute for MS exhibited the highest static yield stress, and fastest re-flocculation and structuration rates, resulting in the best buildability. Although the inclusion of 10% MK resulted in enhanced paste strength at 7 and 28 days, increased MK content impeded paste printability due to diminished formation of hydrate phases. Use of 5% MK led to higher M-S-H generation compared to other samples at 28 days, contributing to subsequent strength development. Results demonstrated that optimisation of the MK content in MgO-SiO2 pastes can yield satisfactory mechanical strengths without compromising printability.

The Influence Of Adding Superplasticizer With Time Interval And Variation Of Water Reduction On The Early Strength And Workability Of Concrete

Acceleration of early strength of concrete can be obtained by reducing water in the concrete mixture followed by addition of superplasticizer. The application of the addition of superplasticiser to water-reduced concrete mixtures requires innovation in providing a time lag to produce good workability. This study analyzes the effect of giving a time delay when adding superplasticizer followed by reducing water with certain variations on the workability and early strength of concrete. The results of this research are very important for the concrete industry with the purpose of shortening the removal time of formwork and optimizing the construction process. Water cement ratio is adjusted by reducing its volume by a fraction of 10% to 30%, superplasticizer 1% to the weight of cement is added in two stages, during the initial mixing and after one or two hours afterwards. 0.3% retarder was added to control homogeneity during mixing. The test results concluded that the reduction of water that provided the highest increase in concrete compressive strength at 4 days was LN25-1 of 21.94 MPa (87% of the design compressive strength) and LN20-2 of 19.12 MPa (76% of the compressive strength plan). The optimal amount of water reduction at the initial age of the concrete is 20 – 25% of the design water weight. Giving a time lag does not reduce the increase in concrete strength due to the addition of superplasticizer.

Low-heat & early-strength well cement system: Application of HSA in hydrate layer cementing

Aiming at the problem that cement hydration heat release easily leads to hydrate decomposition when cementing deep water hydrate layer in the ocean. Heat storage agent (HSA) was prepared, and a cementing system that can be used in hydrate layer was proposed by using early-strength cement and heat storage agent. The research objective is to reduce the hydration temperature of cement on the basis of ensuring the early strength of the cement system so as to meet the cementing needs of the hydrate stratigraphic. In this study, a new heat storage agent was invented and its performance tested. The properties of different proportions of early-strength cement and Class G cement were compared. The performance changes of the cement system after adding heat storage agent were tested. The test results show that heat storage agent can resist the corrosion of seawater and alkali. After heat storage agent is added to the early-strength cement system, the hydration temperature of the cement can be greatly reduced, and the low-temperature (4 °C 24h) compressive strength can reach 5.1 MPa. The microscopic test shows that heat storage agents only affect the hydration rate and temperature of cement without affecting its stability. The results proved that the heat storage agent can be used as an environmentally friendly regulator of the heat of hydration for oil well cement. The results proved that the heat storage agent can be used as a regulator of the heat of hydration of oil well cement.