Compressive Strength Of Cement-based Materials Research Articles

Study on the properties and microstructure of polymer modified waste printed circuit board cement-based materials

Waste printed circuit boards (WPCB) are solid waste, and the current disposal of WPCB in landfills has raised environmental concern. Existing studies used ground WPCB as a replacement of fine aggregate in cement-based materials, but the performances of those materials were notably decreased. This paper aims to improve the performance of WPCB-bearing cementitious materials using styrene butadiene rubber (SBR) latex and chloroprene rubber (CR) latex. For this purpose, cement-based materials with ground WPCB as fine aggregates were prepared, and the effects of SBR latex and CR latex on the mechanical properties of WPCB-bearing samples with varying dosages were studied. The influence mechanism was studied using SEM, hydration heat, XRD, and FTIR tests. The results showed that the incorporation of ground WPCB tends to significantly reduce the compressive strength of cement-based materials, while the addition of SBR and CR latex can prevent the strength loss. For instance, with the optimal dosage of 5 % for SBR latex or 7.5 % for CR, the 28-d compressive strength of the latex-modified sample was 42.6 MPa and 45.3 MPa, which was 26.78 % and 34.82 % higher than that of the unmodified samples. Through microstructure analysis, it was found that the incorporation of WPCB had a negative impact on the densification of cement-based materials. SBR latex and CR latex promoted the hydration reaction and formed continuous film products inside the structure, which improved the bonding performance of WPCB cement-based materials.

Molecular dynamics study of the mechanical properties of hydrated calcium silicate enhanced by functionalized carbon nanotubes.

The incorporation of functionalized carbon nanotubes can enhance the mechanical properties of cement-based materials. However, the types of functional groups and their roles in composite materials are not yet clear. In this study, molecular dynamics (MD) simulation methods were employed to investigate the mechanical performance of hybridized calcium silicate hydrate gel reinforced with pure carbon nanotubes, epoxy-coated carbon nanotubes, carboxylated carbon nanotubes, and hydroxylated carbon nanotubes. The results indicate that the addition of all four types of nanotubes can enhance the mechanical properties of hydrated calcium silicate gel compared to pure C-S-H. Tensile loading results show that carbon nanotubes can act as bridges for microcracks in the composite material, and functionalized nanotubes exhibit a better reinforcing effect than pure carbon nanotubes. Under tensile stress, hydroxylated nanotubes are more effective in increasing the toughness of the composite material, while carboxylated nanotubes tend to enhance the strength of the composite material. The compressive loading results indicate that the compressive strength of cement-based materials is higher than their tensile strength. Overall, carboxylated nanotubes show particularly remarkable performance in enhancing the mechanical properties of cement-based materials. Compared to pure C-S-H gel, the tensile and compressive elastic moduli of carboxylated nanotube/C-S-H composite material increased by 18.13% and 34.78%, respectively. Its tensile and compressive strengths also increased by 30.40% and 40.23%, respectively. All molecular dynamics simulations were performed on the classical computational simulation platform LAMMPS. In this paper, the parameters in the ClayFF force field are chosen to simulate calcium hydrated silicate (/C-S-H), and the ClayFF-CVFF combined force field is used to simulate the mechanical properties of the CNT/C-S-H molecular model structure.

Compressive strength evaluation of cement-based materials in sulphate environment using optimized deep learning technology

Strength serves as a vital performance metric for assessing long-term durability of cement-based materials. Nevertheless, there is a scarcity of models available for predicting residual strength of in-situ structures made of cement-based materials exposed to sulphate conditions. To address this challenge, this study presents a novel approach using deep learning to predict the degradation of compressive strength of cement-based materials under marine environments. Specifically, a deep convolutional neural network (DCNN) is established, consisting of two convolutional layers, one pooling layer, and two fully connected layers. In this innovative model, contents of cement, water-to-cement ratio, sand, sulphate concentration and exposure temperature are selected as inputs, while the output is strength of cement-based materials subjected to sulphate deterioration. To improve the forecast capability, particle swarm optimization is adopted for optimizing hyperparameters of DCNN, which can be implemented by reducing the discrepancy between model prediction and measured strength. Finally, experimental data are used to establish and evaluate proposed method. The results show that the proposed deep learning-based predictive model has the best performance of strength degradation prediction of cement-based materials suffering from sulphate attack via a comparison with other commonly used models. The outcome of this research offers a potential solution for predicting remaining strength of cement-based materials that undergo practical sulphate attack.

Study on the flowability and strength of cement-based materials added with limestone powder and PVA fiber

In order to improve the mechanical properties of cement-based materials, limestone powder (LP) was used as a filler as 0% to 20% cement paste replacement by volume in the mortar. Polyvinyl alcohol (PVA) fiber with 0% to 0.6% by volume were added to produce multiple sets of cement-based materials for basic mechanical properties tests including flowability, compressive strength and tensile strength. The test results indicated that an increase in the amount of PVA fiber and the replacement amount of LP continuously reduce the flowability of cement-based materials. PVA fiber led to the most significant reduction effect. The addition of an appropriate amount of PVA fiber can improve the tensile and compressive strength of cement-based materials, but excessive addition has a negative impact on the compressive strength. When the increase in replacement ratio of LP, the compressive strength of cement-based materials increased. Comparatively, the decrease in tensile strength is not significant.

Machine learning prediction of compressive strength of concrete with resistivity modification

Machine learning techniques can predict the compressive strength of cement-based materials with good accuracy and learning capacity. Traditional compressive strength prediction according to machine learning techniques such as the support vector machine (SVM), decision tree, and Gaussian regression are normally based on the mix proportion of concrete compositions. Resistivity can realize the long-term, real-time and in-situ monitoring of compressive strength of the concrete structures. Therefore, electrical resistivity is regarded as a key nondestructive testing parameter to improve the accuracy of the compressive strength prediction model according to machine learning techniques in this study. When the resistivity was taken into consideration as an input variable accounting for 0.166, the fitting degree of the compressive strength in the decision trees model is increased from 0.77 to 0.79. In the SVM model, the fitting degree remains 0.79, the RMSE decreases from 8.490 to 8.335, which indicates the reliability is improved. The fitting degree in the Gaussian model model is increased from 0.81 to 0.82. As a new parameter variable, the accuracy of the compressive strength prediction model modified with electrical resistivity can be significantly increased. Therefore, the nondestructive testing method can be combined with machine learning techniques to promote the development of civil engineering building structure monitoring, diagnosis and facilitate the development of intelligent buildings through data-driven approaches.

Experimental study of cement-based materials under sulfate attack environment using Electrochemical Impedance Spectroscopy

In this paper, electrochemical impedance spectroscopy tests and compressive strength tests were employed to investigate the sulfate attack process of cement-based materials, and the change law of the electrochemical impedance spectrum with erosion time was analyzed. Based on the typical equivalent circuit model of cement-based materials and its microstructure equivalent circuit model, the change law of electrochemical parameters and its relationship with compressive strength were analyzed. The experimental results indicate that with increasing erosion time, the electrochemical impedance spectrum shows significant quasi-Randles characteristics, its position moves to the right, and the diameter of the high-frequency semicircle increases. The values of RCP, reflecting disconnected pores, and RCCP, reflecting connected pores, increase continuously during the attack process. The compressive strength of cement-based materials reaches a maximum at a sulfate concentration of 55 g/L. The electrochemical parameter RCCP well reflects the compressive strength of cement-based materials and further characterizes the deterioration of its macro properties.

Mechanical properties, durability and microstructure of cementitious materials with low-calcium circulating fluidized bed fly ash

To enhance the utilization of circulating fluidized bed fly ash in construction materials, this study investigated the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the properties of cement-based materials. In addition, an alkali activator was added to improve the properties of cement-based materials mixed with LCFA and the synergistic effect was also investigated. The results show that an appropriate amount of LCFA can improve the compressive strength of cement-based materials in underwater curing conditions. The addition of LCFA can improve the physical properties and carbonization resistance of cement-based materials. Whereas, the addition of water glass (WG) can appropriately shorten the setting time and effectively increase the compressive strength of cement mixtures with LCFA. In addition, adding WG can effectively improve the resistance of chloride ion penetration and carbonation. It is speculated that adding appropriate amount of LCFA enhanced the amount of hydration products generated, filled the coarse pores, and made the pore structure of samples more compact. Appropriate addition of LCFA and WG increases the concentration of hydroxyl groups in the system, accelerates the rupture of Si-O and Al-O bonds on the surface of LCFA particles, and forms free and unsaturated active bonds on the surface of LCFA, which is easier to react with Ca(OH)2 to form hydration products such as C-S-H and C-A-S-H. At the same time, gelatinous hydration products migrate and diffuse with the change of ion concentration in the system, and gradually fill and compact the internal structure.

Strengthening Mechanism for the Mechanical Properties of Cement-Based Materials after Internal Nano-SiO2 Production.

This study focuses on overcoming the agglomeration issue of nano-SiO2 powder in cement, facilitating the strengthening mechanism of cement-based materials. A nano-SiO2 precursor solution (NSPS) was added to cement-based materials to replace nano-SiO2 powder. The influencing laws of the alkalinity and dosage of the NSPS on the mechanical properties of cement were investigated. Further, the strengthening mechanism of the mechanical properties of cement-based materials after internal nano-SiO2 production was analysed. The results show that (1) when the alkalinity of the precursor solution is a weak acid (pH = 6), the compressive strength of cement-based materials after internal nano-SiO2 production is 25%~36% higher than that of pure cement-based materials and 16%~22% higher than that of cement-based materials with silica fume; (2) when the solid content of SiO2 in the current displacement solution is about 0.16% of the cement mass, the compressive strength of the prepared cement-based material is the highest. With the continuous increase in the solid content of SiO2 in the precursor solution, the compressive strength of cement-based materials after internal nano-SiO2 production decreases but is always greater than the compressive strength of the cement-based material mixed with nano-SiO2 micro powder. According to a microstructural analysis, nano-SiO2 particles that precipitate from the precursor solution can facilitate the hydration process of cement and enrich the gel products formed on the cement particle surface. In addition, new network structures among cement particles are formed, and precipitated nano-SiO2 particles fill in the spaces among these cement particles as crystal nuclei to connect the cement particles more tightly and compact the cement-based materials. This reinforces the mechanical properties of cement-based materials.

Predicting compressive strength of cement-based materials containing water-absorbent polymers considering the internal-curing region

The water-absorbent polymer will bring large holes and the internal-curing region for cement-based materials. These two effects will bring negative and positive effects on the compressive strength of the cement-based material, respectively. In this paper, a calculation model of the compressive strength of cement-based materials with water-absorbent polymers was proposed considering the influence of the large holes and internal-curing on the compressive strength. A method for determining the internal-curing width of water-absorbent polymers based on backscattering image analysis was established. Based on the internal-curing width, the compressive strength was predicted and compared with the results of experiments. In addition, the influences of the internal-curing width, size, dosage, mass swelling rate, and volume swelling rate of water-absorbent polymers on the compressive strength were analyzed. The results show that the internal-curing width of the water-absorbent polymers with a mass swelling ratio of 4.22 g/g is about 13 µm. Based on the internal-curing width obtained by characterization, the compressive strength obtained by model is 7 % greater than that obtained by experiments. Besides, the influence range of the internal-curing width, size, and mass swelling ratio of the water-absorbent polymers on the compressive strength is between 80 Mpa and 90 Mpa. The influence range of the dosage and the volume swelling rate of the water-absorbent polymers on the compressive strength is between 20 Mpa and 90 Mpa. The compressive strength is mainly related to the dosage and the volume swelling rate of water-absorbent polymers. The larger the dosage and volume swelling rate are, the smaller the compressive strength is.

Sustainable use of waste eggshells in cementitious materials: An experimental and modeling-based study

This study evaluated the compressive strength (CS) of cement-based materials (CBMs) incorporating eggshell powder (ESP) as a partial substitute for cement and fine aggregate using both experimental and machine learning (ML)-based strategies. Initially, the CS of CBMs based on ESP was measured experimentally. ML techniques, including support vector machine and bagging regressor, were applied for CS estimation. Comparing the coefficient of determination (R2), statistical checks, k-fold evaluation, and measuring the difference between experimental and projected CS were used to evaluate the performance of ML models. According to the results of the experiment, the addition of ESP increased the CS of CBMs when used in lower replacement ratios. In addition, the support vector machine model had a reasonable degree of precision, while the bagging regressor model predicted the CS of ESP-based CBMs with a higher degree of precision. Incorporating waste eggshells into building materials will promote sustainable development by minimizing environmental problems connected with eggshell disposal, conserving natural resources, offering cost-effective materials, and decreasing CO2 emissions. In addition, the use of ML approaches will benefit the construction sector by facilitating efficient and economical ways of analyzing the properties of materials.

The study of effect of carbon nanotubes on the compressive strength of cement-based materials based on machine learning

There are many factors that affect the compressive strength of carbon nanotubes/ cementious composites. However, there is a lack of comprehensive research on the effect of various properties of CNTs on the compressive strength of cement-based materials. In this paper, machine learning was used to predict the compressive strength of single system and multi-system of cement-based materials mixed with CNTs, and the optimal parameters of CNTs properties were also determined. Linear Regression (LR), Support Vector Regression (SVR), Random Forest (RF) and Extreme Gradient Boosting (XGB) were used to predict the compressive strength of the cement paste, mortar and concrete(single system) respectively. The results showed that the R2 of prediction of RF and XGB models was greater than 0.9 for all three systems, and the accuracy of XGB was higher. The data of the three systems were combined into a new dataset(multi-system), RF and XGB were used for its prediction. The results indicated that the same prediction errors were achieved by RF and XGB, and the R2 was 0.93. SHAP model was utilized to explain the prediction results. The analysis of single system showed that the content and diameter of CNTs had obvious effects for all the three systems, and the influence degree of CNTs in concrete was less than that of paste and mortar. Some optimal parameters of CNTs were determined by the multi-system SHAP results: the optimal values of the length and diameter of CNTs were 20 μm and 25 nm, and the content should be within 0.1 %.

Compressive properties of cementitious composites reinforced by 3D printed PA 6 lattice

The lattice-reinforced cementitious composites prepared by placing 3D printed lattices in cementitious matrix has been proved to be effective in improving the bending mechanical properties of cement-based materials, such as improving ductility and brittleness. However, the compressive properties of 3D printed lattice-reinforced cementitious composites are still an open question. In this paper, the compressive properties of 3D printed polyamide 6 (PA6) lattice-reinforced cementitious composites with different structural forms were studies. Six kinds of lattices were fabricated by multi jet fusion (MJF) technique. The volumes of these lattices are identical to ensure that the volume enhancement ratio of the lattices in the cementitious composite specimen is the same. The plain cementitious matrix without lattice was set as the control group, and two nondestructive testing methods, AE and DIC, were used to compare the compressive properties between plain cementitious matrix and lattice-reinforced cementitious composites with different structural forms. The experimental results show that the 3D printed lattice can significantly improve the mechanical properties and failure modes of cement-based materials under uniaxial compression. In contrast, the six lattice forms used in this study can improve the maximum compressive bearing capacity and deformation capacity of the cement-based materials under uniaxial compression test, and reduce the damage of cement-based materials in the elastic deformation stage. This paper confirms that 3D printed lattices can improve the compressive properties of cement-based materials and provide a new method for improving the compressive strength of cement-based materials. At the same time, it provides new ideas for the development of ideal substitutes for steel bars in corrosive environments, energy conservation and emission reduction and the development of green buildings.

Compressive Strength Enhancement in Early Age Acid Activated Mortars: Mechanical Properties and Analysis

To increase the hydration reaction rate and the amount of hydration products, different types and proportions of acids were mixed into mortars. The effects of the acid type and content on the early compressive strength of cement-based materials and the strengthening mechanism were assessed via X-ray diffraction and Fourier-transform infrared spectrum analyses. The addition of acetic acid or hydrochloric acid significantly increased the compressive strength of mortars at 1 d and 3 d, and slightly increased it at 28 d. With increasing acetic acid content, the strengthening effect increased first and then decreased with the best content at 4%. With increasing hydrochloric acid content, the strengthening effect decreased gradually with the best content at 2%.

Towards Sustainable Construction Materials: A Comparative Study of Prediction Models for Green Concrete with Metakaolin

Cement-based materials are widely used in transportation, construction, national defense, and other fields, due to their excellent properties. High performance, low energy consumption, and environmental protection are essential directions for the sustainable development of cement-based materials. To alleviate the environmental pressure caused by carbon emissions in cement production, this paper studies cement-based materials containing metakaolin by a comparison of prediction models for the compressive strength. To more accurately evaluate the compressive strength of metakaolin cement-based materials, this paper compares the prediction effects of four models, namely, support vector machine (SVM), decision tree (DT), k-nearest neighbor (KNN), and random forest (RF), with hyperparameters optimized by the Firefly Algorithm (FA) to study the compressive strength of cement-based materials containing metakaolin. The results demonstrated that the RF model showed the optimized prediction effect considering the lowest RSME value and the highest R value among the hybrid models for predicting metakaolin cement-based materials’ compressive strength. The importance test showed that the cement grade and the water-to-binder ratio greatly influence the compressive strength of cement-based materials with metakaolin compared to the other design parameters.

Research on the sulfate resistance of cement-based materials incorporating dolomite powder

The effects of dolomite powder on the sulfate resistance of cement-based materials with water-binder ratio (w/b) of 0.55 and 0.36 were investigated in this manuscript. Scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and pressure testing machine were used to determine the apparent morphology, micro-morphology, mass increase rate, flexural strength and compressive strength of cement-based materials containing dolomite powder. The sulfate resistance of mortars was improved with increasing dolomite powder dosage. Generally, the flexural strength and compressive strength of mortars in Na2SO4 solution were higher than those in water. Within 150 days of immersion, the corrosion resistance coefficient and compressive corrosion resistance coefficient of mortars increased with increasing dolomite powder dosage. The pore structure of cement-based materials became more compact with the addition of dolomite powder. Accordingly, the sulfate resistance was improved by controlling the dynamics stage due to the fact that the pore structure of cement-based materials was refined with the addition of dolomite powder. The 150-day compressive corrosion resistance coefficients of mortars with a w/b of 0.55 in the case of dolomite powder at 0 and 30 wt% replacement levels were less than 1, suggesting that long-term immersion in sulfate solution increased the deterioration rate of cement-based materials.

Relationship Between Microscopic Pore Structure and Strength of Cement-Based Materials with Low Water-Binder Ratio Under Sulfate Attack Environment

In this paper, the mass loss test, relative dynamic elasticity modulus test, compressive strength test, thermogravimetric analysis (TGA-DTG), and mercury intrusion porosimetry (MIP) were used to study the performance of cement-based materials with low water-binder ratio after sulfate attack, and the influence of microsilica dosage and erosion period on the performance was also investigated. The results indicate that the microsilica mixed can improve the macro-properties of cement-based material with low water-binder ratio after sulfate attack, and as the microsilica dosage is increased, the improvement effect tends to decrease after an increase, while the microsilica dosage is 15%, all performance indexes are the best. This study also demonstrates that the microsilica dosage could affect the mass percent and pore structure distribution of the hydration products of cement-based materials with low water-binder ratio after sulfate attack, and different pore structure distribution may have impact on compressive strength of cement-based materials. Besides, we established relation models for the influence of capillary pores’ and gel pores’ proportion on the compressive strength of cement-based material after sulfate attack, and concluded that there was no interaction between the impacts of two pore types on compressive strength.

Investigation of Low-Calcium Circulating Fluidized Bed Fly Ash on the Mechanical Strength and Microstructure of Cement-Based Material

This present study mainly focuses on the influence of low-calcium circulating fluidized bed fly ash (LCFA) on the mechanical property and microstructure of cement-based materials under different curing conditions. The mechanical properties test was conducted by changing variable parameters, such as LCFA content, the internal mixing ratio of LCFA and fly ash (FA), and dry and water curing conditions. Further, the hydration products and pore structure were analyzed using XRD, FT-IR, TG-DTG, NI, SEM, and BET micro-testing technology. The strength development law of LCFA on cement-based materials is discussed. The research results show that LCFA has a certain degree of self-hardening and can be used as a cementitious material in cement-based materials. Still, the loose and porous microstructure of LCFA leads to higher water requirements, which reduces the fluidity of cement-based pastes. Water curing is favorable for promoting the development of LCFA on the long-term compressive strength of cement-based materials. When the LCFA was added to the cement, the optimal substitution ratio was 20%, and the compressive strength at 91 days reached 101 MPa. In the case of compounding LCFA and FA, when the internal mixing ratio of LCFA/FA was 3 and the total content was 20%, the mechanical properties were the highest, and the compressive strength at 91 days was 92 MPa. The microscopic analysis result shows that the cumulative hydration heat of the samples decreased significantly with the increase of dosage of LCFA. The main hydration products of cement-based materials mixed with LCFA were AFt, C-S-H gel, and Ca(OH)2. AFt and C-S-H gels are critical to the strength development of OPC-LCFA samples. The active Al2O3 and active SiO2 in LCFA were involved in hydration reactions to promote the formation of C-A-H and C-S-H gel and effectively promote the development of the mechanical properties. Overdosages of LCFA would reduce the ettringite formation rate. FA is not conducive to AFt formation in the hydration process of OPC-FA samples.

The Study of Effect of Carbon Nanotubes on the Compressive Strength of Cement-Based Materials Based on Machine Learning

The Study of Effect of Carbon Nanotubes on the Compressive Strength of Cement-Based Materials Based on Machine Learning

Predicting Compressive Strength of Cement-Based Materials Containing Hydroabsorbent Polymers Considering the Internal-Curing Region

Predicting Compressive Strength of Cement-Based Materials Containing Hydroabsorbent Polymers Considering the Internal-Curing Region

Water distribution and transport-kinetics model in fresh cement-based mixtures containing superabsorbent polymers based on 1H low-field NMR

Superabsorbent polymer (SAP) can be used as a curing agent in cement-based materials. Due to the replenish of humidity decline caused by the continuous consumption of water, the SAPs will contribute substantially to mitigating the shrinkage and obtaining the expected curing efficiency. Many studies have described the characteristics of water immigration in SAP-modified cement-based mixtures, but the travelled distance, volume, and transport-kinetics model of the water released from the SAP in cement-based materials still need to be investigated in detail. The paper focuses on the sustained water distribution of SAP at early-age cement-based mixtures. The swelling characteristics of SAP in different liquids and the water transport kinetics in hydrating cement-based mixtures were studied based on the ion concentration test and low-field Nuclear Magnetic Resonance (NMR) measurement. The results show that when SAP is in contact with water or cement filtrate, the exchangeable cations on the SAP structure will move freely to the solution and rapidly exchange with the metal cations in the solution within a few minutes (about 5 min). The most predominant form of water in fresh cement-based mixtures was the absorbed water (adsorbed on the surface of particles or in pores). Part of the adsorbed water or small capillary water on the surface of cement particles was consumed for hydration. The incorporation of SAP can prevent bleeding and segregation and promote the 28-day compressive strength of cement-based materials under the same total w/c ratio. Finally, the water-transport model in fresh cement-based mixtures was established and verified.