Curing Ages Research Articles

A Study on Choosing Bricks on Site During Construction

Large numbers of bricks are required to meet the needs of increasing population for both residential and commercial sectors. The overall development and industrial development lead to the use of the traditional bricks at a very hefty rate. The traditional bricks are commonly made up of clay as its main component as a result it is on the verge of exhaustion. To standardize its broad, utilize and discovering its auxiliary one is the need of the hour. In this study, bricks were made by using different proportions of alternative materials like fly ash(FA), sand, lime and plaster of Paris . The size of sample 220×130×900 mm was manufactured and quality constraints like compressive strength and water absorption were tested at different curing ages. The cost-effective mix design of the bricks for optimum compressive strength and rate analysis was also the part of this study. It was detected from the observation of results that the compressive strength decreases with increasing percentage in fly ash and increases with increasing percentage of sand and lime in fly ash-based bricks. Increment in water absorption was observed as fly ash content is increased and decrement of water absorption is seen with increasing percentage of sand and lime in fly ash-based bricks.

Experimental study on the basic properties of new biomass bamboo aggregate concrete

Gravel aggregate is an important part of concrete, but the resources of natural aggregate, such as gravel, are increasingly scarce and may have adverse effects on the environment. Therefore, a new biomass bamboo aggregate concrete was proposed in this study, which bamboo aggregate was used to replace gravel aggregate to alleviate the shortage of gravel resources. To study the basic properties of bamboo aggregate concrete and explore its feasibility, tests for compressive strength, splitting tensile strength, flexural strength, and uniaxial compressive stress-strain curve were conducted. The microstructure was also observed. The research parameters included the concrete curing age and different bamboo aggregate volume replacement ratios. The results presented that the mechanical properties of bamboo aggregate concrete were enhanced with increasing age. Compared with the normal concrete, the mechanical properties of bamboo aggregate concrete decreased as the replacement ratio of modified bamboo aggregate increased, but the 28-d compressive strength of modified bamboo aggregate concrete could still reach 74% of that of normal concrete. The mechanical performance of bamboo aggregate concrete was significantly influenced by whether bamboo aggregates were modified. The uniaxial compressive stress-strain model proposed by GB50010-2010 was suitable for bamboo aggregate concrete. The interfacial bonding effect between modified bamboo aggregate and cement matrix was improved.

Using thermokinetic methods to enhance properties of epoxy resins with amino acids as biobased curing agents by achieving full crosslinking

Fibre-reinforced polymers (FRPs) are used in numerous industrial sectors and contribute to reducing CO2 emissions due to their outstanding properties in lightweight design. However, sustainable alternatives must be developed since the matrix polymers utilised contain substances hazardous to health and the environment. In widely used epoxy resins, the curing agents are mainly critical. Using biomolecules instead of synthetic curing agents can significantly reduce composites' toxicity and petrol-based carbon content. This study considerably exceeds the thermo-mechanical properties of epoxies cured with amino acids described in the literature until now. It demonstrates competitive or even better properties than state-of-the-art epoxies cured with petrol-based amine curing agents. For instance, the tensile strength of arginine-cured epoxy is more than twice as high as reported before and 13.5% higher compared to the petrol-based reference. At the same time, a high elongation at break of over 6% was accomplished, making these polymers suitable as matrix materials in FRPs. Furthermore, the glass transition onset of up to 130 °C is sufficiently high for many applications. The key to success is the development of individual curing profiles based on thermokinetic analysis. The work provides the development and analysis of several biomolecule-cured epoxies with promising property spectra.

Optimization and mechanism analysis of a compound additive for unfired bricks made of construction and demolition wastes

Construction and demolition waste (CDW) was fully exploited to prepare high-strength and low-cost unfired bricks. A compound additive consisting of sodium silicate, microsilica powder, an early-strength water reducer, and wood fiber was incorporated into the bricks. Tests (compressive tests, freeze–thaw cycle tests, and scanning electron microscopy (SEM)) were carried out to determine the effect of the contents of the additive components on the properties (the strength, softening coefficient, freezing resistance, hydration products, and microscopic morphology) of unfired bricks of different curing ages. The experimental results were used to determine the optimum ratio of the components and the hydration mechanism. The optimized compound additive considerably improved the mechanical properties and crack resistance of the bricks, where the optimum content was found to be only 3.15% of the CDW dry mass. Compared with unfired bricks with no additives, unfired bricks with the optimized compound additive exhibited increases in the 1- and 28-day compressive strengths and softening coefficient of up to 66.8%, 65.9%, and 8.46%, respectively (corresponding to values of 8.46 MPa, 29.36 MPa, and 0.934, respectively) and a decrease in the freeze–thaw strength loss rate of 61.38%. Incorporating the compound additive into the unfired bricks considerably reduced the environmental impact. The SEM micrographs showed that the compound additive increased the silicon-to-calcium ratio and workability of the preparation mixture, increased the hydration rate, promoted the conversion of calcium hydroxide in the product to a C–S–H gel, and enhanced the density and strength of the hydration product.

Suitability of Using LA Abrasion Machine for the Nano Manufacturing of Palm Oil Fuel Ash and Incorporating in Mortar Mixture

Background In order to enhance the properties of palm oil fuel ash-based mortar, researchers have explored the concept of reducing palm oil fuel ash (POFA) to a nanoscale. While previous studies have utilized ball milling machines with high grinding speed to achieve nano-scale POFA, the Los Angeles abrasion machine, which is more readily available and has a slower grinding speed, has been rarely employed. Objective The study aimed to investigate the suitability of using a Los Angeles abrasion machine with a low grinding speed to produce nano palm oil fuel ash. This paper also provides a comparison of the effect of using the nano POFA with different particle sizes within the range of 982 to 150 nm on the mortar’s flowability and compressive strength. Methods To produce nano-size palm oil fuel ash using the Los Angeles abrasion machine, the received palm oil fuel ash was thermally treated and ground using a Los Angeles abrasion machine with varying grinding periods. The grinding process parameters were kept constant, but second grinding periods of 50,000, 80,000, and 110,000 cycles were introduced. All three types of nano palm oil fuel ash were analyzed for their physical properties, chemical properties, morphology, and mineralogy. Furthermore, these nano palm oil fuel ashes were incorporated into a designed mortar mix along with micro palm oil fuel ash. The mortar’s fresh properties and compressive strength at different curing ages were observed and analyzed. The relationship between various factors, such as the replacement rate of micro, nano palm oil fuel ash, the grinding cycles of nano POFA, and the corresponding responses, specifically the compressive strength at different curing ages, was analyzed and explained using the response surface methodology. Results The 110k cycle nano palm oil fuel ash had a smaller particle size of 103.1 nm, while a particle size of 529 nm and 325 nm was found in the 50k and 80k cycle nano palm oil fuel ash. In terms of the combination of micro and nano palm oil fuel ash in the mortar, increasing the dosage of nano palm oil fuel ash contributed to improvements in flow diameter and compressive strength. However, the opposite trend was observed with micro palm oil fuel ash. The optimal mix design for the combination involved using 10% micro and 2 to 3% nano palm oil fuel ash. This composition led to an improvement rate of 7.9%, 1.48%, and 4.6% in compressive strength at 7, 28, and 90 days, respectively. While, the response surface methodology’s numerical optimization also supported the use of a similar combination. However, it additionally recommended employing the 50,000-cycle nano palm oil fuel ash in the mortar for earlier curing stages, while the 110,000-cycle nano palm oil fuel ash was suggested for later curing stages. Conclusion Los Angeles abrasion machine could be utilized to produce nano palm oil fuel ash with a particle size up to 103 nm with the aid of designed parameters. In this mortar mix design, the impact of a small variance in nano palm oil fuel ash’s particle size was trivial compared to the replacement rate of micro palm oil fuel ash on the mortar’s compressive strength.

Mikrostruktur, Porositas Dan Sifat Mekanik Beton Curing Air Laut

When constructing buildings in coastal areas, contact between the materials used and sea air is sometimes unavoidable. Before the concrete reaches its maximum strength at the age of 28 days, it can be exposed to contamination from sea air. Consequently, chemical reactions involving cement, air, and sea air become inevitable. The research aims to ascertain the microstructure, porosity, and mechanical properties (compressive strength and tensile strength) of high-performance concrete utilizing the Self Compacting Concrete method. Two variations of concrete samples are considered, involving differences in the curing water used and the age of the concrete. There are two curing variations: concrete cured with fresh water and concrete cured with seawater. The concrete's age is monitored at 1, 3, 7, 28, and 90 days. In the microstructure analysis of seawater-cured concrete, chloride compounds, ettringite, and Friedel's salt were identified. Both compressive strength and splitting tensile strength show an increase with the concrete curing age, and they are inversely proportional to the concrete's porosity. The mechanical properties of freshwater-cured concrete are slightly lower than those of seawater-cured concrete. However, the difference is negligible, meaning they are nearly identical at both 28 days and 90 days.

Research on the influence of dispersed carbon nanomaterials with different water reducing agent in cementitious mortar

In this paper, the dispersion of Carbon nanomaterials (CNMs) in an electrolytic solution containing cations such as Ca2+, Al3+, Na+, and Mg2+ with different types of superplasticizers (Sika, Master Ease 3502, Prime DC, and Prime Flow) have been investigated. Further, the stabilized CNMs along with different superplasticizers (Sps) incorporated into the cementitious mortar and studied their mechanical strength. The influence of Sps on the stability of CNMs in an aqueous medium has been monitored by UV-Visible spectroscopy. The study concludes that Sika Sp was the best dispersant for the CNMs dispersion in an aqueous medium. The de-stability of the CNMs has followed this trend of the agglomerations in the electrolytic solution as Al3+>Ca2+>Mg2+>Na+. The Sika Sp has great dispersant properties as well as provides a homogeneous distribution of CNMs in a cementitious matrix which was supported by FE-SEM analysis. The addition of SIKA@PPC-GO (GO about 0.0015% by weight of cement) and SIKA@PPC-FCNTs (FCNTs about 0.0015% by weight of cement) results in enhancement of cement 11.67%, 8.73% for compressive and 26.35, 20.61% for tensile strength respectively, at the curing ages of 90 days. This investigation may provide advanced knowledge to predict the stability of CNMs in superplasticizer-based solutions.

Alkali Tolerance of Concrete Internal Curing Agent Based on Sodium Carboxymethyl Starch

Alkali Tolerance of Concrete Internal Curing Agent Based on Sodium Carboxymethyl Starch

Mechanical properties of uniaxial compression of total tailings paste under lateral restraint effect

After the filling of paste into the mined-out area, significant disparities are evident between the mechanical characteristics and the unconfined conditions, primarily caused by the lateral extrusion of the surrounding rock. To research the mechanical properties of paste under the influence of lateral restraint effect, a device was developed to apply lateral pressure to the paste. This was then combined with an existing uniaxial press machine to carry out uniaxial compression testing of the paste subject to lateral restraint effect. The device was used to carry out uniaxial compression tests under different curing ages and dry and wet conditions under the lateral restraint effect, and compared with the unconfined condition. The study revealed a considerable increase in the paste's strength caused by the lateral restraint effect, resulting in a growth rate ranging from 12.35% to 64.51%. The mathematical model of lateral stress and strength was established, and it was found that the two showed a significant quadratic function relationship. By acquiring the stress-strain data of the loading process, the evolution characteristics of the stress-strain curve of the paste under the influence of the lateral restraint effect are revealed, and the change rule of the elastic modulus is explored. Under the influence of the lateral restraint effect, the growth rate reaches 1.93% to 64.04%. When comparing the crack propagation characteristics of the paste with and without the influence of the lateral restraint effect, it was observed that the failure mode of the paste under uniaxial compression shifts from tensile failure to shear failure. Finally, this paper proposes the strength design method for backfill with considerations to the lateral restraint effect. The reliability of the suggested method is established through actual sampling results in the mine. The research findings hold significant guiding value for the secure and efficient extraction of paste backfill mines.

Effect of Superplasticizer in Cement Type on Morphological Characteristics of Masonry Mortar

Cement plays a crucial role in mortar composition, and its particles exhibit a strong tendency to flocculate when mixed with water. This flocculation necessitates the addition of substantial water to improve the workability of mortar or concrete. However, this extra water does not contribute to the hydration reaction, potentially weakening the mechanical properties of the mortar. The introduction of superplasticizers has addressed this issue by reducing the water demand. Nevertheless, a common practice in construction is to use a standard dosage of superplasticizers for the same type of cement, even when sourced from different cement factories, which may affect material performance. This study investigated the influence of varying superplasticizer dosages on Portland pozzolana cement from different Ethiopian cement factories, examining the morphological characteristics of masonry mortar. Specifically, it evaluated the impact on cracks, porosity, and surface structure across different curing ages, as well as assessed the mortar’s physical and mechanical properties. Mortar samples prepared using cement from three factories, labeled A, B, and C, with constant cement‐to‐sand ratios of 1:3 and water‐to‐cement ratios of 0.5. Superplasticizer added in varying amounts 0%, 0.6%, 0.8%, and 1%. The morphological analysis conducted using a 3D optical surface profiler microscope at 1, 7, 21, and 28 days. Besides these standard physical and mechanical tests also performed on all samples. The results demonstrated that addition of superplasticizers significantly influenced the surface morphology of mortar samples. Mortars A and B exhibited denser structures with superplasticizer dosages 0.8% and 1%, respectively, whereas mortar C displayed a denser structure in its control state (without superplasticizer). The flexural and compressive strength tests also revealed notable differences. Sample A2 (0.8%) from group A, sample B3 (1%) from group B, and sample C0 (0%) from group C achieved the highest strength within their respective groups at 28 days. The findings suggest that it is essential to evaluate the specific properties of cement before applying a standardized superplasticizer dosage, as variations in cement production can significantly influence the performance of the mortar.

The pore structure and water absorption in Portland/slag blended hardened cement paste determined by synchrotron X-ray microtomography and neutron radiography.

The pore structures of hardened Portland/slag cement pastes (>75 wt% slag content), and the initial capillary absorption of moisture through these pores, were monitored using ex situ synchrotron X-ray computerised microtomography and in situ quantitative neutron radiography. The pore structure becomes more constricted as the cement hydrates and its microstructure develops. This mechanism was effective even at a slag content as high as 90 wt% in the cementitious blend, where the lowest total porosity and a significant pore refinement were identified at extended curing ages (360 d). By combining this information with neutron radiographic imaging, and directly quantifying both depth and mass of water uptake, it was observed that 90 wt% slag cement outperformed the 75 wt% slag blend at 90 days in terms of resistance to capillary water uptake, although the higher-slag blend had not yet developed such a refined microstructure at 28 days of curing. The assumptions associated with the "sharp front model" for water ingress do not hold true for highly substituted slag cement pastes. Testing transport properties at 28 days may not give a true indication of the performance of these materials in service in the long term.

Optimization of mix proportion and strength prediction of magnesium phosphate cement-based composites based on machine learning

In order to optimize the mix ratio design of magnesium phosphate cementitious composites (MPCC) to obtain excellent workability and strength, this study investigated the effects of MgO-phosphate ratio, water-binder ratio, aggregate-binder ratio, the mass ratio of coarse and fine aggregates, mineral admixture content and steel fiber content on the flowability, setting time and cubic compressive strength (CCS) of MPCC using orthogonal design of experiments with a total of 32 sets of mix ratios. The experimental results were also analyzed utilizing range and variance analysis to determine the main influencing parameters and the optimal dosage of each factor, and the optimal MPCC mix ratio was obtained. In addition, the prediction of CCS for MPCC using five machine learning models was first introduced, and the predicted results were interpreted and analyzed regarding the SHAP (Shapley Additive exPlanations) features importance. The results showed that the effect of steel fiber volume content and water-binder ratio on the flowability was significant, and M/P significantly affected the setting time of MPCC. The CCS of MPCC increased with the age of curing, and MPCC exhibited high early strength, with 1-day CCS accounting for 55%～85% of the 28-day CCS. The effect of M/P on the 1-day, 3-day and 28-day CCS was highly significant, with M/P contribution rate as high as 76.3%, 80.3% and 83.6% of the CCS at 1, 3 and 28 days, respectively. Besides, the effect of steel fiber volume content on 28-day CCS was also significant. In summary, the optimal mix ratio of MPCC was A4B1C4D1E4F4G1 (M/P = 3, w/b=0.11, a/b=1.4, c/f=3, FA content =15%, MK content= 15%, steel fiber volume content= 0%). Furthermore, random forest (RF) and particle swarm optimization of back propagation artificial neural network (PSO-BP-ANN) models have a higher prediction accuracy, and the results of SHAP feature significance further confirmed the above test results.

Effect of internal curing by superabsorbent polymers on the densification and microstructural development of cementitious materials exposed to different environmental conditions

Superabsorbent polymers (SAPs) are among the internal curing agents used in cementitious materials. This study aims to evaluate the influence of wider SAP dosages under different exposure environments on the microstructural densification of cementitious materials and the development of strength and durability based on this. With SAP incorporation, hydrate crystallization most easily occurs in the wet/dry condition through hydration with externally supplied water and by internal SAP curing, which leads to the formation of the densest microstructures. Microstructure densification further progresses as the SAP dosages increase. Despite the internal curing effect of SAPs, the ultrasonic pulse velocity and the compressive strength of S0.5 specimens compared with those of the REF specimens decrease due to SAP void presence. However, these mechanical properties of the S1.0 specimens are all recovered at later ages when exposed to the wet/dry condition, forming densest microstructures. As the SAP dosages increase, the sealing effect of SAPs improves the water permeability characteristics at early ages. The lowest water permeability coefficient is observed in the S1.0 specimen exposed to the wet/dry condition as the further hydration effect of SAPs is exerted with increasing ages. In conclusion, utilizing the appropriate amount of SAPs and environmental conditions can effectively densify the internal pore structures, thereby securing the mechanical and durable properties of concrete structures.

Research progress of geopolymer solidification / stabilization of heavy metal contaminated soil

As a new type of green and environmentally friendly aluminosilicate gel material, geopolymer has attracted much attention from scholars for its good ability to immobilize heavy metals compared with traditional cement-based curing agents. Based on the research progress of geopolymer solidification of heavy metal contaminated soil at home and abroad in recent years, this paper introduces the process of geological polymerization reaction. The solidification mechanism of geopolymer on heavy metal contaminated soil and the influence of different factors on the solidification effect of geopolymer on heavy metal contaminated soil are described in detail. The leaching characteristics of heavy metals in geopolymer solidified heavy metal contaminated soil under freeze-thaw cycle, dry-wet cycle and carbonization were further discussed. Finally, the problems existing in the solidification of heavy metal contaminated soil by geopolymer are analyzed and the future research and development direction is prospected.

Effect of enhanced pozzolanic activity in nickel slag modified with Al2O3 on mechanical properties of cemented fine tailings backfill

Cemented tailings backfill has gained widespread acceptance in mining industries due to its stable performance and environmental advantages. However, Ordinary Portland cement (OPC), based on engineering experience, falls short in meeting the requirements of cost-effectiveness and environmental protection criteria for cemented fine tailings (median size d50 <20 µm) backfill. Nickel slag (NS), an industrial solid waste with potential reactivity derived from nickel manufacturing processes, is currently employed as a concrete additive at a low rate. In this work, a modification was conducted by melting-quenching the NS-Al2O3 mixtures, followed by a physicochemical analysis of the resulting granulated samples (GAN) using BET and X-ray fluorescence. The mineralogy and structural properties were examined for the GAN samples using X-ray diffraction and Fourier transform infrared spectroscopy. Each of the T-CGAN pastes was formulated by replacing 40 wt% of OPC with the GAN, and then blended with fine tailings at 1:4. The flowability and compressive strength were measured for the T-CGAN pastes, while the hydration products and microstructures of the paste samples were analyzed by derivative thermogravimetry and scanning electron microscope, respectively. The results indicate that the addition of Al2O3 not only provides abundant network formers to GAN glass, but also facilitates the conversion of [SiO4] tetrahedrons from Q4 with strong bond energy to Q3 and Q2 with lower ones, thereby significantly enhancing the pozzolanic activity of the original NS. The T-CGAN slurries exhibit slight decreases in slump values from 228.8 to 224.9 mm compared to T-OPC slurry (236.5 mm), attributed mainly to the strong water absorption of GAN. T-CGAN pastes with higher Al2O3 addition acquired greater compressive strengths during the whole curing ages. After 90 days of curing, T-CGAN20 paste achieves the maximum compressive strength (5.14 MPa), higher than that of the T-OPC by 1.03 MPa. The T-CGAN pastes richer in Al2O3 release more reactive Si and Al to participate in the pozzolanic reaction with calcium hydroxide, contributing to additional formations of C-S-H gel and C-A-H, with SEM micrographs showing a compact microstructure with elevated ratios of Ca/Si, Al/Si, and Fe/Si. This study suggests an effective and environmental way to enhance the pozzolanic activity of the original NS by incorporating Al2O3. The modified NS can then be utilized as a high-performance cement substitute for cemented fine tailings backfill, which also significantly enhances the sustainability for both mining and building industries.

Experiment on Compressive Properties and Microscopic Analysis of Sea Sand Geopolymer-Based Recycled Concrete.

For marine and coastal engineering, construction resources have become scarce due to a limited local supply. Sea sand geopolymer-based recycled concrete (SSGRC) is an innovative cementitious material known for its eco-friendly benefits and corrosion resistance. This study explores the mechanical properties of SSGRC. The influences of the replacement rate of mineral slag, alkali activator concentrations, fine aggregate types, and curing ages on the compression strength of SSGRC were studied. The failure mechanism was analyzed using the failure patterns and compressive stress-strain curves. The results show that sea sand had a positive effect on geopolymer-based material. The SSGRC reached peak strength with an alkali activator concentration of 10 mol/L and a mineral slag replacement rate of 60%. The maximum stress and strain increased with an increasing curing age. The ratios of strength to the peak value were 55% and 85% after 1 day and 7 days, respectively. Using SEM, in the last hydration stage, the C-(A)-S-H gel was formed with a dense microstructure, and the geopolymer exhibited a favorable bonding performance. The constitutive models describing the complete stress-strain relationship under compression were developed.

Experimental study on solidification/stabilization of leachate sludge by sulfoaluminate cement and MSWI by-products.

Leachate sludge is generated from the biochemical treatment sludge tank for disposing the leachate from landfill municipal solid waste (MSW). It has the characteristics of high water content and high organic matter content. Sulfoaluminate cement (SAC) is used as the main curing agent, and municipal solid waste incineration (MSWI) by-products are used as auxiliary curing agents to solidify/stabilize the leachate sludge. The influences of SAC content and MSWI by-products content on the strength and solidification mechanism of the leachate sludge are investigated by unconfined compressive strength (UCS) test and micro-observation tests. Moreover, the leaching concentration of heavy metals of the solidified samples is analyzed by leaching toxicity test. The results show that the UCS of the solidified samples increases with an increase in cement content. When the cement content is larger than 20%, the UCS of the solidified samples satisfies the strength requirement of landfill. The enhancing effect of bottom ash on the cement-solidified samples is slight. The fly ash is a good auxiliary curing agent for improving the UCS of cement-solidified samples, and the optimal dosage of fly ash is 5% and 15% for the solidified samples with 10 ~ 30% and 40 ~ 50% cement content, respectively. Ten percent fly ash can replace 10% cement to achieve better solidification effect for the solidified samples. The leaching concentration of heavy metals in the solidified sample with 30%/40% cement and 15% fly ash/bottom ash can satisfy the strength and leaching toxicity requirements of landfill. The immobilization of heavy metal of the cement and MSWI by-products solidified samples is mainly achieved through physical adsorption, physical encapsulation, ion exchange, and chemical precipitation.

Feasibility study on preparation of fully-waste building blocks using alkali-activated materials to solidify construction and demolition waste residue: Formulation optimization and reaction mechanism

As a by-product of the construction and demolition waste (CDW) classification process, the construction and demolition waste residue (CDWR) faces the problem of having nowhere to be stacked and being unable to be handled. Solidifying CDWR by alkali activation technology to make building blocks not only provides a value-added method for recycling CDWR, but also promotes the sustainable development of rural construction. In this study, a new alkali-activated material (NAAM) was proposed for the solidification of CDWR, and the optimal ratio of NAAM at different curing ages was determined by mixture design, and then the micro-mechanism and macro-properties of CDWR solidified with NAAM were investigated. The results show that the compressive strength of the optimized specimen at 14-day meets the requirement of 10 MPa. After solidifying CDWR with NAAM, the products generated are mainly calcium silicate hydrate gels with different morphologies, accompanied by ettringite and CaCO3. Water content and pH have a significant impact on the compressive strength, and low water content and pH value have a negative impact on the pozzolanic reaction and the generation of products of the specimen. In general, it is feasible to use NAAM mainly composed of waste brick powder proposed in this paper to solidify CDWR. Without using cement and natural aggregates, it still shows good mechanical property and environmental benefits.

Feasibility study on superabsorbent polymer (SAP) as internal curing agent for cement-based grouting material

The closed working condition of grouting materials leads to insufficient curing water supply during their strength development. In this work, the superabsorbent polymer (SAP) was used as the internal curing agent for grouting material. The effects of SAP content on the rheological and mechanical properties of grouting material were studied under various water-cement ratios (w/c) and curing environments. The time-dependent variation of fresh slurry's viscosity was measured by Brinell viscometer. The pore structure and micromorphology characteristics were analyzed by Mercury Intrusion Porosimetry (MIP) and Scanning Electron Microscope (SEM). The results indicate that the addition of SAP increases the viscosity of fresh slurry and decreases its fluidity, thereby improving the slurry's internal uniformity at a higher w/c. And in its actual working condition, grouting material's strength can be boosted with less than 0.3% SAP dosage. Although SAP will introduce some irregular mesoscopic pores (0.2 − 0.3 mm), the MIP data analysis proves SAP refines the microscopic pore structure of grouting materials. SEM data analysis proves SAP optimizes the microstructure of grouting material, which cured in dry environment. In general, SAP improves the internal uniformity of grouting material by absorbing excess mixing water and gradually releasing it to promote cement hydration, which improves the strength of grouting material. Hence, SAP is a practicable internal curing agent for grouting material and 0.2% is the recommended dosage.

Impact resistance of geopolymer concrete under different types of fiber admixtures

To investigate the dynamic mechanical response characteristics of geopolymer concrete under impact load, the effects of different curing ages and strain rates on the impact resistance of geopolymer concrete have been explored. First, this paper first obtains the optimal mix ratio of geopolymer concrete by optimizing the slump test of mix ratio. Second, the stress–strain constitutive relationship of geopolymer concrete at different ages is deduced, and the mechanical properties, such as axial compressive strength and elastic modulus, are determined. Finally, two different kinds of fibers, carbon fiber and steel fiber, are mixed into concrete, which are utilized to test the mechanical properties including compressive strength, splitting tensile strength, flexural strength, and impact toughness. The results indicate that with the increase in carbon fiber content, the compressive strength, splitting tensile strength, and flexural strength of geopolymer concrete decrease first and then increase. Moreover, with the increase in steel fiber content, the compressive strength of geopolymer concrete increases continuously, the splitting tensile strength increases first and then decreases, the flexural strength decreases first and then increases, and the impact toughness increases first and then decreases.