High Early Compressive Strength Research Articles

Effects of NaHCO3 as the activator and the in-situ carbonate seeding on the properties of high-dosage Ca(OH)2 + slag (HCHS) cement

This study investigated the effects of the addition of NaHCO3 (5, 10, and 15% molar amount of Ca(OH)2) on the setting time, compressive strength, drying shrinkage, and hydration process of high-dosage Ca(OH)2 + Slag (HCHS) cement. The results indicated that the NaHCO3 addition could significantly increase the 1-day compressive strength of HCHS cement from almost 0 to 10 MPa and decrease the drying shrinkage of HCHS cement up to 46.1% compared to it without NaHCO3. But the addition of NaHCO3 above 5% would result in accelerated setting, increased porosity, and decreased strength in the later stages. NaHCO3 played an in-situ carbonate seeding effect, forming CaCO3 crystals through the initial reaction of Ca(OH)2, and the activator that increased solution alkalinity promoted the formation of hydration products. These could contribute to the HCHS cement with high early compressive strength, good volume stability and certain porosity, suitable for further carbon capture.

Experimental study on application performance of foamed concrete prepared based on a colloidal NanoSiO2-stabilized foam

In this study, colloidal nanoSiO2 (CNS) was added into the foaming agent at 0, 0.5, 1, 1.6, and 2 wt% of the binder mass to enhance the stability of foaming agent and prefabricated foam, further the stability of foamed slurry and hardened foamed concrete. First, the stability of CNS on foaming agent and prefabricated foam was investigated by examining surface tension, surface viscoelastic modulus E, foam parameters, surface shear viscosity, and morphology. Prefabricated foam containing CNS was then used to prepare foamed concrete with a dry density of 700 kg/m3. The rheological characteristics, volume change, setting time, hydration properties, and gas content for fresh foamed slurry and the pore characteristics, compressive strength, and thermal conductivity of hardened foamed concrete were characterized. The microstructural crystalline structures of the foamed slurry and hardened foamed concrete were also investigated. Results of this study indicated that nanoSiO2 nanoparticles in colloidal state improved the stability of foam, especially when the CNS dosage was ≥ 1 wt%, because CNS caused increases in the surface viscoelasticity modulus E of the foaming agent and the surface shear viscosity of the prefabricated foam. Moreover, foamed slurry with a shorter hydration induction period, more stable volume, a shorter initial setting time, and higher viscosity was obtained when the CNS dosage was ≥ 1 wt%. Hardened foamed concrete with higher early compressive strength and superior thermal insulation properties was correspondingly obtained when fresh slurry with higher stability was used. However, the effect of CNS will decrease on the compressive strength of the hardened foamed concrete after 14 days of hydration. Finally, mechanisms were proposed regarding the stabilization effects of CNS on the prefabricated foams, foamed slurry, and hardened foamed concrete.

Improvement of early strength of structural lighweight concrete using large volumes of Ground-Granulated Blast Furnace Slag

This paper presents the experimetal results on the influence of chemical additive, i.e. Ca(NO¬3)2, on the compressive strength of structural lighweight concrete (LWC) containing high volume ground-granulated blast-furnace slag (GGBFS). Structural LWC using 27% (by vol. of concrete mixture) fly ash hollow microspheres, also known as cenosphere (FAC) is used up to 27% by volume of concrete mixture with a density in the range from 1.600 to 1.900 kg/m3, compressive strength over 40 MPa. Achieving high early age compressive strength is difficult and challenging for lightweight concrete with high volume GGBFS. Therefore, the present study focused on the influence of Ca(NO3)2 on the strength development (under curing condition of 27 ± 2oC and relative humidity of 60 ± 5%) of structural LWC containing 50, 65 to 80% GGBFS (replacing cement content by weight). The experimental results show that the addition of Ca(NO3)2 enhanced the early-age compressive strength of structural LWC up to 11,6% and 9,0% at the age of 3, 7 days, respectively.

Performance and hydration of ternary cements based on Portland clinker, carbonated recycled concrete paste (cRCP) and calcined clay

This study explored composite cements consisting of Portland clinker, two pozzolans (alumina-silica gel in carbonated Recycled Concrete Paste (cRCP) and metakaolin), and calcium carbonate. The rapid reactivity of alumina-silica gel resulted in full reaction within 28 days, while metakaolin exhibited slower reactivity. cRCP played a significant role in strength development between 1 and 7 days, with metakaolin becoming prominent thereafter. The combination of materials preserved their distinct characteristics. Early hydration was mainly influenced by clinker and cRCP, leading to high early compressive strength. After alumina-silica gel dissolved, metakaolin forms a microstructure, reducing porosity and allowing for continued strength improvement over time. The pozzolans did not hinder their respective reactions, and calcium carbonate from cRCP stabilized ettringite content, similar to limestone-calcined clay systems. This study’s findings offer insights for developing multi-component cement with cRCP and calcined clays, resulting in higher strength and reduced CO2 footprint compared to calcined clay-limestone cements.

The Effect of RHA and GBFS on the Mechanical and Physical Properties of Cementitious Composites with High Early Age Compressive and Flexural Strength: Bayesian Algorithm for the Design

The Effect of RHA and GBFS on the Mechanical and Physical Properties of Cementitious Composites with High Early Age Compressive and Flexural Strength: Bayesian Algorithm for the Design

High early strength foamed concrete design for structural precast concrete

Precast lightweight concrete with specific gravity between 1440 kg/m3 and 1840 kg/m3, and high early compressive strength is one of the alternative materials in responding to the large and fast demand for precast concrete, as well as being easy to transport. This study proposes high early strength foamed concrete as an alternative to precast lightweight concrete for residential construction. The background of this study is considering the limited literature reports related to research on precast foamed concrete for the application of building structural elements. The purpose of this study was to obtain high early strength foamed concrete for structural precast concrete with minimum characteristics, including initial compressive strength of 14 MPa at 3 days of age, 20 MPa of compressive strength at 28 days of age, and specific gravity of less than 1750 kg/m3. There are 3 types of foamed concrete was studied, namely normal foamed concrete, foamed concrete with LDPE, and foamed concrete with water substitution accelerator. Then, compressive strength testing was conducted on cylindrical specimens. The results showed that foamed concrete with 10% water substitution accelerator produced the highest values for the initial compressive strength of 3 days and 28 days of age, 21.64 MPa and 29.27 MPa, respectively, and the specific gravity of 1743 kg/m3.

Flue gas carbonation curing of steel slag blocks: Effects of residual heat and water vapor

To make full use of residual heat (temperature) and water vapor (relative humidity, RH) retained in flue gas, the compound effects of temperature (60–140 °C) and RH (2–60 %) of 2-hour CO2 curing on the compressive strength and CO2 fixation of basic oxygen furnace slag (BOFS) blocks were systematically investigated. The results indicated that, in general, an increase of curing temperature increased the compressive strength of the blocks. The high early compressive strength gain (31.3 MPa) at 2-hour for carbonated BOFS blocks was directly related to the microstructure densification and pore refinement due to rich formation of calcite. It should be noted that the supply of sufficient water vapor (≥40 % RH) is particularly important at high temperature (e.g. ≥ 120 °C) to offset the water loss due to water evaporation. Furthermore, under an extremely dry environment (2 % RH), the continuous flow-through of CO2 gas at high temperature not only resulted in no carbonation reaction at the outer layer of the freshly pressed blocks, but may also deteriorate the integrity of the pore structure matrix.

A novel CO2 foaming agent for the preparation of foamed sulfoaluminate cement material: Application to coal mine filling

High-risk areas in coal mines have become an increasingly serious issue in recent years. However, the chemical foaming agents used in coal mine filling management are mostly hydrogen peroxide which produces combustible O2 and aluminum or zinc powder which is explosive H2. All of the above chemical foaming agents do not have safe filling conditions. In this paper, we propose a new inorganic foaming material that generates inert gas CO2. Foamed sulfoaluminate cement-based grouting material (FSCGM) was prepared by chemical foaming. The expansion capacity of CO2 foaming agent was studied. The effects of W/C, foaming agent admixture, and Lime/Anhydrite (L/A) on expansion times, foaming time and setting time were studied and the optimum proportion of FSCGM was determined. The mechanical properties, durability, and fire prevention performance of the FSCGM with the optimal proportion were studied and simulated filling tests were conducted. The results showed that the CO2 foaming agent with 30% dosing expands 8.8 times after 10 min of foaming. The best proportion of W/C was 2.2, CO2 foaming dosing was 25%, L/A was 3:5, 6 h compressive strength was 0.52 MPa, 7 d water absorption rate was 46.2%, softening coefficient was 0.75. With the increase of foam admixture and W/C, the CO2 concentration gradually increased, and the fire prevention effect became more apparent. After simulated filling, the slurry did not collapse the mold, the expansion times was 1.74 times, and the dry density of the sampled specimens was about 0.3 g/cm3. It is observed that the bubbles were evenly distributed, and the hole structure was small and dense. Therefore, we prepared FSCGM with ultra-low density, high early compressive strength, and good fire prevention performance by using novel CO2 foaming agent. In addition, the feasibility results indicate that the FSCGM has great potential for engineering applications.

The potential of one-part alkali-activated materials (AAMs) as a concrete patch mortar

One-part alkali-activated materials (AAMs) are developed to improve conventional two-part systems. One-part AAMs technology has been used in cement binders to produce concrete, mortar, and paste. Current research mainly focuses on synthesizing raw materials obtained from industrial and agricultural waste as the main aluminosilicate precursors of the cement binder for a concrete application. The one-part AAMs were reported to have higher early compressive strength at 7 days of age, contributed by its fast-setting time, mainly when the binder activates by a higher dosage of alkaline activator and containing OPC-rich. Due to bonding issues, single or combination, FA/GGBFS/MK precursors were reported as unsuitable for use as a concrete repair material. They were the reason for the lack of one-part AAMs application of mortar compared to concrete usage. This study was conducted to determine the potential of one-part AAMs used as concrete patch mortar by investigating its rheology and mechanical properties. The compressive strength of the mortar was tested under lab ambient temperature in the tropical climate country of Malaysia. The setting time of fresh mortar and bonding strength were set under controlled lab temperature. The one-part alkali-activated mortar was composed of hybrid aluminosilicate precursors between fly ash (FA), Ground Granulated Blast Furnace Slag (GGBFS) and ordinary Portland cement (OPC). A low alkaline activator of solid potassium carbonate was used for the geopolymerization process. Three types of solid admixtures were added to complete the composition of the new mix design. The experiment's outcome showed that the mortar composed with the combination of conventional Portland cement and industrial waste products has compressive and pull-off adherence strength that meets with Class R3—EN1504-3 standard for structural concrete repair materials requirement.

Retrofitting RC beams using high-early strength alkali-activated concrete

Demolition of existing deteriorated structures and construction of the new structures is a costly, time-consuming, and resource-intensive process. Repair of concrete beams and strengthening techniques for existing reinforced concrete elements is a resource-saving exercise that is time-saving also. In this work, a repair material using metakaolin-based alkali-activated concrete (AAC) is developed with high early compressive strength and split tensile strength designed with proper mix proportions. The flexural strength of reinforced concrete beams was determined without the new repair material. The specimens were loaded until failure and the deflected portion of the RC beam was then confiscated using breakers. The confiscated portion is subsequently replenished with metakaolin-based AAC and flexural strength and bond characteristics were determined. Shrinkage length changes were also measured. The metakaolin-based AAC with 15% metakaolin had a high stiffness and increased flexural strength up to 14.4% compared to the specimen before repair. It also exhibited a significant bonding with the concrete substrate with less shrinkage and improved strength.

High-Performance Fiber Reinforced Concretes in Virginia

High-performance fiber reinforced concretes (HPFRCs) provide high workability, high compressive and tensile strengths, high ductility, and high durability. They exhibit strain and deflection hardening. The Virginia Department of Transportation (VDOT), U.S., has been experimenting with various types of HPFRC, including high early strength versions, to control cracking in transverse and longitudinal connections, shear keys, blockouts that connect adjacent members, overlays, and inverts of corrugated metal pipe culverts. This paper presents laboratory and field work using three classes of HPFRC for different VDOT applications. They have high ductility and very low permeability. In addition, Class I has normal compressive strength, Class II has high compressive strength, and Class III has high early compressive strength. Laboratory work consisted of preparing and testing of in-house or prepackaged HPFRC with varying ingredients and proportions using compression, indirect tension, flexure, and pull-out tests. Synthetic and steel fibers were added in different amounts. Mixtures were prepared in the mortar or pan mixers that produce good fiber dispersion. Laboratory and field testing indicated that all three classes of HPFRC had high ductility; strengths varied according to the class. Engineered cementitious composite in Class I had normal strength, ultra-high-performance concrete in Class II had the highest strength, and concretes in Class III had high early strength, enabling minimal traffic interruption. HPFRC selected from an appropriate class can be used successfully to enable early opening to traffic, provide a short splice length, achieve satisfactory adjacent member connections, and restrict crack width for a longer service life.

Mechanical activation of diabase and its effect on the properties and microstructure of Portland cement

Many volcanic rocks with pozzolanic properties are used as additives in cement production. Although diabase is a volcanic rock, it has not been used as an additive material in cement production until now. In this study, pozzolanic reaction ability, mechanical, hydration and microstructure properties were investigated before and after mechanical activation in order to increase the usability of diabase in cement production. Firstly diabase samples were analyzed for chemical, mineralogical compositions and pozzolanic activity. The diabase was first subjected to dry grinding separately from clinker to increase the amorphous structure by decreasing its crystalline structure and mechanical activation was achieved.The pozzolanic activity of the ground diabase gradually increased depending on the grinding time. The effects of 10%, 30% and 50% addition of natural diabase by weight on the characteristics of cement pastes and cement mortars were researched. Zeolite containing cliptonolite mineral was used as a comparison material with diabase. The Blended cement specimens were tested for particle size, setting time, water demand, soundness, heat of hydration, and compressive strength. The compressive strength proportion of the cement mortar samples containing large quantities of natural diabase were lower than that of the Portland control cement at all tested ages up to 28 days, but it was a higher compressive strength than zeolite blended cements. 10%, 30% and 50% diabase blended cements and 10%, 30% and 50% zeolite blended cements give results above the Cem IV 32.5 R standards. 10%, 30% and 50% diabase blended cements have achieved high early compressive strength than zeolite blended cements. 10%, 30% and 50% diabase blended cements have achieved low final compressive strength than zeolite blended cements. In addition, diabase blended cements may produced at approximately 5% lower cost than zeolite blended cements. All results proved that diabase may be a good alternative to new generation mineral additives in producing cement.

CO2 pretreatment of municipal solid waste incineration fly ash and its feasible use as supplementary cementitious material

In this study, municipal solid waste incineration fly ash (MSWIFA) was pretreated with CO2 via slurry carbonation (SC) and dry carbonation coupled with subsequent water washing (DCW). Both the treated MSWIFAs were then used as cement replacement in cement pastes by weight of 10%, 20% and 30% to investigate the influence on hydration mechanisms, physico-mechanical characteristics and leaching properties. The results showed that carbonates formed on the surface of SC-MSWIFA particles were finer (primarily 20–50 nm calcite) than those from the corresponding DCW-MSWIFA (mostly 130–200 nm vaterite). Hence, SC-MSWIFA blended cement pastes led to shorter setting time and higher early compressive strength than the DCW-MSWIFA pastes. In contrast, the presence of vaterite-rich DCW-MSWIFA in the blended cement pastes could accelerate the cement hydration after 24 h. Both the CO2-pretreated MSWIFA can replace cement up to 30% without sacrificing the long-term strength and mechanical properties of cement pastes, demonstrating excellent performance as a supplementary cementitious material. Moreover, volume stability in terms of expansion and lead leaching of CO2-pretreated MSWIFA cement pastes were far below the regulatory limits.

Modification of high-volume fly ash cement with metakaolin for its utilization in cemented paste backfill: The effects of metakaolin content and particle size

High-volume fly ash (FA) cement presented a slow setting and lower early compressive strength, restricting the utilization in cemented paste backfill (CPB). The present work investigated the feasibility of using metakaolin with various particle sizes and content to modify the properties of FA cement. Reaction kinetics, rheological properties, setting time, compressive strength, hydration products, and the CPB samples' microstructure were thoroughly studied. The results showed that 5 wt% of super-fine metakaolin (SMK) could strongly promote the binder hydration, leading to the formation of a more compact matrix with higher early compressive strength. The 3 d-compressive strength of the CPB samples was increased by around 216% after replaced by 5 wt% of SMK. Besides, the binder doped with 5 wt% SMK showed better environmental and cost performance.

EFFECTS OF COLD JOINT AND ITS DIRECTION ON THE COMPRESSIVE AND FLEXURAL STRENGTH OF CONCRETE

A cold joint is the main problem in concrete construction, especially in large quantities such as mass concrete. The capacity of mixing plan and manpower make monolith casting is impossible. The distance between the batching plant and the construction location is also an obstacle to cold joints. This study would test the compressive and flexural strength due to the effect of cold joint in concrete. The period of the casting between two concrete (cold joint) was 120 minutes and 240 minutes. Tests carried out in the form of compressive strength and flexural strength of the vertical and horizontal directions of cold joints. The types of concrete used in this study include normal concrete with 35 MPa compressive strength, concrete with high initial compressive strength using superplasticizer, and concrete using polypropylene fiber as added material. Compressive and flexural strength tests were carried out at 3, 7, 14 and 28 days. All specimens used water curing up to the predetermined test life. The test results show that specimen with the cold joint connection in normal concrete has a decrease in quality (flexural and compressive), so does with the concrete with superplasticizer (high early compressive strength), whereas in concrete using fiber has increased in strength compared to normal concrete without cold joint connection.

Mechanical degradation of ultra-high strength alkali-activated concrete subjected to repeated loading and elevated temperatures

In this work, a clinkerless alkali-activated slag-based ultra-high strength concrete (AAS-UHSC) with tailored mix proportions was developed at room temperature. To evaluate its practical serviceability, a systematic investigation was conducted on the fresh and mechanical properties (compressive, splitting tensile, and flexural strengths), with an emphasis on the uniaxial compressive behavior of AAS-UHSC subject to repeated loading and elevated temperatures. The results showed that despite the fast setting of AAS-UHSC, a significant improvement in flowability could be obtained with a slight increase in water-to-binder ratio. Regarding the strength development during the curing period, a higher early compressive strength was observed for AAS-UHSC when compared with ordinary Portland cement (OPC)-based UHSC, but a contrary behavior was found for the evolution of splitting tensile strength. Moreover, relative to the fiber-free AAS-UHSC, great improvements up to 31 times and 2.5/4.3 times in the flexural fracture energy and monotonic/cyclic compressive toughness were achieved for the specimens containing 1.5% steel fiber by volume, respectively. The superior high-temperature performance of AAS-UHSC free of explosive spalling could be attributed to its intensive shrinkage cracking upon dehydration, which likely leads to a significant enhancement of pore connectivity as the exposure temperature increases.

Preparation and properties of a magnesium phosphate cement with dolomite

Calcined dolomite containing free-CaO cannot be directly applied in magnesium phosphate cement (MPC) as magnesia raw materials. To chemically combine with CaO and replace magnesite, dolomite-bauxite-gypsum (DBG) powders were calcined to produce MPC containing ye'elimite. The properties of the calcined DBG powders obtained at calcination temperatures no higher than 1300 °C were studied. The performance of these MPC pastes prepared with calcined DBG powders and the hydration process of the new system were also investigated. Results showed that the calcined DBG powders were mainly composed of magnesia, ye'elimite and belite. MPC pastes with calcined DBG powders exhibited high early compressive strength and good volume stability. Ye'elimite was confirmed to participate in the hydration reactions and would also improve the water resistance of the MPC pastes. Some new amorphous hydration products containing Al-P in mesh-like structures were observed during water curing and might be beneficial for the compressive strength development.

Estimating the Impact of Nanophases on the Production of Green Cement with High Performance Properties.

Ordinary Portland cement (OPC) production is energy-intensive and significantly contributes to greenhouse gas emissions. One method to reduce the environmental impact of concrete production is the use of an alternative binder, calcium sulfoaluminate cement, which offers lower CO2 emissions and reduces energy consumption for cement production. This article describes the effect of adding nanophases, namely belite, calcium sulfoaluminate, calcium aluminum monosulfate (β-C2S, C4A3S, and C4AS, respectively) on OPC’s properties. These phases are made from nanosubstances such as nano-SiO2, calcium nitrate (Ca(NO3)2), and nano-aluminum hydroxide Al(OH)3 with gypsum (CaSO4·2H2O). The impact of β-C2S, C4A3S, and C4AS nanophases on the capabilities of cements was assessed by batch experimentations and IR, XRD, and DSC techniques. The results showed that the substituting of OPC by nano phases (either 10% C4A3S or 10% C4A3S and 10% β-C2S) reduced setting times, reduced the water/cement ratio and the free-lime contents, and increased the combined water contents as well as compressive strength of the cement pastes. The blends had high early and late compressive strength. The IR, XRD, and DSC analyses of the blends of 10% C4A3S or 10% C4A3S and 10% β-C2S cement displayed an increase in the hydrate products and the presence of monosulfate hydrate. The addition of 10% C4AS or 10% C4AS and 10% β-C2S to OPC reduced the setting times, decreased the W/C ratio, free lime, the bulk density, and increased the chemically-combined water and compressive strength. Overall, the results confirmed that the inclusion of the nanophases greatly enhanced the mechanical and durability properties of the OPCs.

Early-age strength property improvement and stability analysis of unclassified tailing paste backfill materials

High-density tailings, small cementitious materials, and additives are used for backfill materials with poor early compressive strength (ECS), which may greatly affect the mining and backfill cycle, to prepare paste backfill materials (PBMs) with a high ECS. The effects and mechanisms of different early strength agents on the property of PBM are investigated. The action mechanism of additives on the properties of PBM is also analyzed through X-ray diffraction, scanning electron microscope, and energy dispersive spectrometry. Results show that the effects of single-component additives 1, 3, and 6 are better than those of the other additives, and their optimal dosages are 3wt%, 1wt%, and 3wt%, respectively. The optimum multicomponent combinations are 1wt% of additive 1 and 1.5wt% of additive 6. The ECS of the paste with additive 10 increases to a greater extent than that of the other pastes because of the synergistic action of additive 1 with additive 6. The hydration product of Ca(OH)2 is consumed, and more C-S-H gels are generated with the addition of additives to paste. Tailings particles, ettringite crystals, and gels intertwined with one another form a dense net-like structure that fills the pores. This structure can significantly improve the ECS of PBM.

Utility of local quartz powder and silica fume to produce high early strength of self compacting high strength concrete

Generally concrete needs 7 to 14 days to reach minimum adequate compressive strength. Sometimes it is needed to get high early compressive strength of concrete for some reason. This research conduct an experimental program to make high early strength of self compacting concrete which is using local quartz powder and silica fume. Twenty one cylinder specimens were made and tested to get the compressive strength at age of 1 day, 3 days, 7 days, 14 days, 21 days, and 28 days. While the modulus elasticity of concrete were tested only at the age of 28 days. The cylinder specimen was using standard size of (150 × 300) mm2. The experimental program shows that the average compressive strength of concrete in 1 day, 3 days, 7 days, 14 days, 21 days, and 28 days were 10.00 MPa, 27.16 MPa, 36.41 MPa, 40.93 MPa, 50.36 MPa, and 48.66 MPa, respectively. While the average modulus elasticity of the concrete at the age of 28 days was 18,703.45 MPa.