Compressive Strength Ratio Research Articles

Influence of carlin-type gold mine tailings addition on the synthesis temperature, alkali-resistant performance, and hydration mechanism of Portland cement

The massive discharge of carlin-type gold mine tailings (GMT) has caused serious harm to the environment, such as occupying land and building tailings dams. However, GMT is rich in SiO2 and CaO, which is likely to be a material for the synthesis of Portland cement in theory. Thus, this work synthesized four Portland cement with GMT addition of 0.00, 5.00, 10.00, and 15.00 wt%, and investigated their synthesis temperature, mineral phase composition, alkali-resistant performance, and hydration mechanism via the CaO free test, X-ray diffraction, compressive strength ratio, electron microscopy, and thermogravimetric analyzer. Results show that the synthesis temperature decreases by 100 °C when the GMT addition in raw materials exceeds 10.00 wt%. The mineral phase composition of these synthesized Portland cement is alite, larnite, tricalcium aluminate, and tetra-calcium aluminoferrite; their hydration phase is rod-like AFt, nubby CSH, and sheet-like Ca(OH)2; both are the same as that of Portland cement without GMT. Results also show that the Portland cement synthesized with 10.00 wt% GMT performs better on the compressive strength (24.7/18.5 MPa at 7 days and 56.1/48.6 MPa at 28 days) and alkali-resistant (0.75 at 7 days and 0.87 at 28 days) since the highest output of the total AFt and CSH (8.50/13.25 wt% at 7/28 days) and the Ca(OH)2 (5.89/11.57 wt% at 7/28 days). This work proves that GMT as a material for the synthesis of Portland cement is viable, and provides an effective method for the resource utilization of GMT.

The Effect of CKD and RAP on the Mechanical Properties of Subgrade Soils

The construction of pavement layers on subgrade soil with good characteristics decreases the thickness of these layers, which in turn lowers the cost of building and maintaining roadways. However, it is impossible to avoid constructing pavements on unsuitable subgrade due to a number of limitations. Using conventional additives like lime and cement to improve subgrade properties results in additional costs. As a result, utilizing by-products (cement kiln dust and reclaimed asphalt pavement) in this field has benefits for the environment, economy, and technology. Large amounts of cement kiln dust (CKD), a by-product material, are produced in Portland cement factories. On the other hand, large amounts of reclaimed asphalt pavement (RAP) are accumulated as a result of the rehabilitation of old roads. This paper discusses using CKD and RAP to improve the characteristics of poor subgrade layers by conducting a series of Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) tests on samples of natural soil and soil stabilized with different percentages of CKD and RAP with different curing times to investigate their impacts on soil properties. The curing was carried out by wrapping the stabilized samples with several layers of nylon and then placing them in plastic bags at room temperature. The compaction results illustrated that the addition of CKD increases OMC and decreases MDD, in contrast to RAP, which decreases OMC and increases MDD. The addition of CKD and RAP led to a significant and unexpected increase in the CBR values. The results show that the soaked and unsoaked CBR values improve from 3.4% and 12.1% for natural soil to 220.1% and 211%, respectively, after adding 20% CKD and curing the samples for 28 days. Also, the addition of 25% RAP to soil-20% CKD blend increased the soaked and unsoaked CBR values to 251% and 215%, respectively. All the additions resulted in a significant reduction in swelling.

Characteristics of mixed-mode Ⅰ-Ⅱ fracture of bedding mud shale based on discrete element method

Mud shale is an abundant unconventional source of oil and gas, with considerable potential for extensive exploration and development. Hydraulic fracturing is a core technology for the harvesting of mud shale resources. Mud shale usually contains developed bedding structures. A mixed-mode Ⅰ-Ⅱ failure occurs when hydraulic fractures meet the bedding layers. Understanding the characteristics of the mixed-mode Ⅰ-Ⅱ fracture of mud shale is of high practical significance. A numerical model for a semi-circular bend (SCB) specimen is built using a flat-joint model (FJM). The macroscopic mechanical parameters of the numerical model are calibrated, including the uniaxial compressive strength, elastic modulus, and Poisson's ratio. The microscopic parameters of the model are constantly adjusted using the trial-and-error method to realize an effective fit between the model and rock parameters. The results show variation characteristics of the stress field, displacement field, and fracture toughness are revealed on a microscopic scale during fracture initiation and propagation. The fracture propagation law under different bedding strengths and initial fracture angles is discussed, and the pattern of fracture interactions under different bedding angles and initial fracture angles is obtained. The results showed that the influence of the fracture toughness as the bedding angle decreased. The fracture arrest and the degree of fracture deflection upon reaching the bedding are more considerably influenced by the strength of the weak plane. The higher the bedding strength of the weak plane, the more likely the fractures were deflected in the bedding. However, fracture penetration of the bedding layer is more greatly influenced by the bedding angle.

Monitoring and estimate of concrete compressive strength in full curing period using smart piezoelectric modules

Concrete compressive strength is a most important material performance index and can reflect the quality of a concrete material. An innovative test method is proposed for monitoring the development of concrete compressive strength during the full curing period using smart piezoelectric modules (SPMs). The proposed method overcomes shortcomings of traditional methods and can be used for non-destructive, real-time, continuous, in situ monitoring of concrete strength during the whole curing period. A series of experiments demonstrates the validity and effectiveness of the method using SPMs. The energy values of monitoring signals from SPMs is applied as a characteristic identification parameter for concrete compressive strength. The signal waveform and frequency suitable for monitoring concrete compressive strength are determined, and a standard test procedure using SPMs to monitor concrete compressive strength is defined. Finally, equations for correlating the signal energy ratio and compressive strength ratio of different grades of concrete (i.e., C30, C40 and C50) based on the SPM monitoring data are established. The compressive strength of concrete for the given curing age can be effectively predicted by the proposed method, and the established correlation equations can be applied to assess the concrete condition and strength in curing.

Sustainable development of basalt fiber-reinforced high-strength eco-friendly concrete with a modified composite binder

The aim of the paper is to development of basalt fiber-reinforced high-strength eco-friendly concrete with modified composite binder for sustainable construction. Cement composites based on a modified polymineral binder with the use of enriched aluminosilicates obtained from coal ash have been developed. A technology has been developed for extracting aluminosilicates from coal ash, which includes five stages. The choice of grinding technology of modified composite binder in a vario-planetary mill up to 550 m2/kg has been made, where the combined action of high impact energy, strong friction and centrifugal forces achieves the maximum mechanical activation of the binder. The developed fresh mixes are characterized by good flowability (slump 20 cm and slump flow 47–49 cm). The resulting composites are characterized by high 28-day compressive and flexural strengths of 59.1 and 13.3 MPa, respectively, which is 44% and 66% higher than that of the control sample. At the same time, the high ratio of 28-day flexural and compressive strengths, reaching 0.31 (for the control sample 0.19), proves the high potential of this material to work under shock and dynamic complex loading. These trends are also preserved for the ages of 1 and 7 days, which allows us to speak about the high early strength of the materials. Microstructural analysis using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy showed that the modified cement matrix has a denser microstructure with a large amount of low-basic calcium silicate hydrates (C-S-H), while the reference cement paste contains more high-basic C-S-H and hexagonal portlandite plates. The formed materials are able to withstand up to 15 thermal cycles at a temperature of 700 °С (4 times higher than that of the control sample), 13 thermal cycles at a temperature of 900 °С (4.3 times higher), 8 thermal cycles at a temperature of 1100 °С (exceeding eight times the characteristics of the unmodified sample, which is destroyed without enduring a single thermal change).

Experimental investigation on compressive properties of three-dimensional five-directional braided composites in hygrothermal environment

Abstract This article describes work concerning the compressive properties in hygrothermal environment of three-dimensional (3D) five-directional braided composites. Hygrothermal aging tests at temperatures of 40, 60, and 80°C and compression tests were carried out on the specimens with three braiding angles of 15, 25, and 35°. The surface morphologies of the samples taken using scanning electron microscope before and after the hygrothermal aging test were used to analyze the influence of the hygrothermal environment on the internal structure of braided composites. The experimental results indicate that the hygrothermal environment has a more influence on the specimens with a braiding angle of 15°, and the greater the moisture absorption percentage, the lower the retention ratios of compressive strength and modulus. Compared with room temperature, the compressive strength and modulus of specimens with a braiding angle of 15° reduced by 72.2 and 82.7% as the water bath temperature increased from 40 to 80°C. Moreover, the failure mechanisms of 3D five-directional braided composites in the hygrothermal environment were analyzed.

Expansive behavior of high-strength self-stressing and self-compacting concrete: Experimental study and analytical model

This paper presents an experimental investigation on the expansive behavior of high-strength self-compacting concrete (HSCC) with various HCSA expansive agent (EA) contents ranging from 0 % to 12 %. The fresh properties, compressive strength and expansive ratios at free and restrained conditions are studied. The expansive process and expansive mechanism of self-stressing HSCC are analyzed with a combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Moreover, the self-stress of expansive HSCC under the confinement of steel-tube is measured. The results show that the compressive strength of HSCC decreases with increasing EA contents, which should not be over 12 % due to the large expansions damage the concrete matrix seriously. The expansive ratios increase significantly with increasing EA contents, as well as increasing amplitudes. The free expansive ratios of concrete can reach 1.08 × 10−4, 3.03 × 10−4, 5.13 × 10−4 and 7.85 × 10−4 with the EA content ranging from 6 % to 12 % at 28 curing days, respectively. Moreover, the self-stresses of expansive HSCC with EA contents of 8–12 % are 3.2–3.7 MPa. Finally, under the framework of plane strain model in elasticity theory, a calculation analytical method is developed to predict the restrained expansive ratios of HSCC confined by steel tubes. The computational formula is also established to calculate the self-stress of expansive HSCC using the axisymmetric plane problems in elasticity. The model formula provides a good description of expansive responses of self-stressing HSCC.

Study on Shrinkage Cracking Morphology of Cement Mortar with Different Nanoclay Particles under Restraint

In this paper, different types and particle sizes of nanoclay (nano-metakaolin—NMK—and nano-attapulgite—NMA—clay) were selected to study the effect of nanoclay on the properties of cement-based cementitious materials. The stability of different nanoclay dispersions was analyzed. The effects of nanoclay on the mechanical properties and cracking behavior of cement mortar were discussed. The crack propagation behavior of nanoclay cement mortar was analyzed by flat knife-edge induced constraint and ring constraint experiments. The research shows that the degree of aggregation of NMA particles is lower than that of NMK. The larger the particle size of NMA, the lower the degree of particle aggregation. The larger the particle size of NMK, the lower the degree of particle aggregation in water. NMK has the best improvement effect on cement mortar. The smaller the particle size, the more pronounced the improvement effect. The flexural strength ratio, compressive strength ratio, and elastic modulus ratio of 7 d and 28 d are 76.7%, 67.4%, and 61.2%, respectively. In the flat plate cracking experiment, the maximum crack width of NMK-3 and NMA-2 was reduced by 33.3% and 25.0%, respectively, compared with ordinary cement mortar. The maximum crack length was reduced by 55.1% and 33.1% compared with cement mortar. In the ring constraint experiment, the total cracked area of NMK-1, NMA-1, NMK-3, and NMA-2 rings increased by 64.3%, 45.0%, 92.7%, and 49.7%, respectively, compared with ordinary cement mortar rings after 60 days. NMK can advance the cracking time of cement mortar, but it can inhibit the generation and development of cracks and refine the crack width.

Rock Burst Intensity Classification Prediction Model Based on a Bayesian Hyperparameter Optimization Support Vector Machine

Rock burst disasters occurring in underground high-stress rock mass mining and excavation engineering seriously threaten the safety of workers and hinders the progress of engineering construction. Rock burst classification prediction is the basis of reducing and even eliminating rock burst hazards. Currently, most of mainstream discriminant models for rock burst grade prediction are based on small samples. Comprehensive selection according to many pieces of literature, the maximum tangential stress of surrounding rock and rock uniaxial compressive strength ratio coefficient (stress state parameter), rock uniaxial compressive strength and uniaxial tensile strength ratio (brittleness modulus), and the elastic energy index are used as a grading evaluation index of rock burst based on the collection of different construction engineering instances of rock burst in 114 groups of extensive sample data in different regions of the world, which are used to carry out the training study. The representativeness and accuracy of the index selection were verified by the indicator variance analysis and Spearman correlation coefficient hypothesis test. The Intelligent Rock burst Identification System (IRIS) based on an optimizable SVM model was established using data set samples. After extensive data cross-validation training, the accuracy of the SVM discriminant analysis model can reach 95.6%, which is significantly better than the prediction accuracy of the traditional SVM model of 71.9%. The model is used to classify and predict the rock burst intensity of 10 typical projects at home and abroad. The prediction results are consistent with the actual rock burst intensity, which is better than the discriminant model based on small sample data and other existing prediction models. The application of engineering examples shows that the results of the rock burst intensity classification prediction model based on extensive sample data processing analysis and the SVM discriminant method are in good agreement with the actual rock burst intensity, which can effectively provide a reference for the prediction of rock burst intensity grade in a construction area.

Mechanical properties of lightweight expanded clay aggregate (LECA) concrete

The construction activities are based on structural concrete, which is one of the most commonly used materials. The fundamental aim of using lightweight concrete (LWC) was to reduce the concrete self-weight of the structure parts. As a result, LWC has been used successfully in a variety of installations for several years. In this paper, the mechanical properties of concrete made with lightweight expanded clay aggregate (LECA) as a full replacement for coarse aggregate are studied. The experimental program shows that LECA with a 32 MPa cube compressive strength and an 1,823 kg×m–3 dry density can be used to make structural light-weight aggregate concrete (SLWC). The results show that the reduction in the strength of lightweight aggregate concrete (LWAC) was found to be higher in the concrete with an estimated compressive strength of 32 MPa due to the lower strength of the LWA (expanded clay). According to the test results, the mechanical properties of LWC were greatly improved by adding silica fume (SF). Furthermore, LECA concrete has a splitting tensile strength that is 47% higher than the ASTM C330/C330M-17A minimum requirement. The LECA concrete has a splitting tensile strength to compressive strength ratio of approximately 13%. Additionally, the results demonstrate a 27% difference in the modulus of elasticity between the calculated and tested values.

Seismic performance of a ring–beam connecting concrete-filled steel columns with RC frames

The seismic performance of a ring–beam connection system to integrate concrete-filled steel tubular columns and reinforced concrete (RC) frames was studied. Physical experiments on two specimens were conducted under monotonic and cyclic loading. The results showed the connection system had a displacement ductility ratio of 4.68 and an energy dissipation coefficient over 2.0. A finite-element model was established and the numerical and experimental results were compared in terms of skeleton curves and stiffness degradation trends. Parametric studies were then performed to evaluate the effects of the axial compressive force ratio, concrete strength and reinforcement ratio of the ring–beam joint (RBJ) and the reinforcement ratio of the frame beam on the seismic performance of the proposed RBJ connection system. The results showed that an increase in the axial compression ratio or strength of the concrete material improved the initial stiffness and strength of the connection system. The effects of the RBJ reinforcement ratio and the frame beam reinforcement ratio on seismic performance were negligible.

Analytical study and design approach of the axial and flexural response of reinforced masonry columns confined with FRP jackets

Using fiber-reinforced polymer (FRP) wraps has proven to be an effective and optimized confinement technique to upgrade the axial and flexural capacity of reinforced concrete (RC) and reinforced masonry (RM) columns. The axial capacity of FRP-confined masonry depends on both the compressive strength of masonry before strengthening and the confinement pressure provided by the FRP jacket. This study proposes a simplified methodology to design and analyze prismatic fully grouted reinforced masonry columns (RMCs) strengthened with FRP Jackets. The proposed design methodology included an analytical confinement model to predict the compressive strength gain in RMCs due to the effective confinement pressure provided by FRP jackets. The proposed procedure was also designed to predict the nominal capacity of RMCs for practical design applications, with columns subjected to both axial loading and bending moment. The essential parameters to perform detailed section analysis were established, and suggested expressions were proposed to obtain the parameter values. Practical values for the equivalent rectangular stress block parameters were proposed. The theoretical axial force-moment interaction diagrams obtained by the proposed procedure were compared with available experimental data. The experimental test results were in good agreement with the analytical predictions by a reasonable marginal error. Furthermore, the effect of five design variables on the axial-flexural interaction of FRP-wrapped RMCs was investigated. The variables considered in the parametric study were the number of FRP layers, radius of the corners, stiffness of the FRP composite, cross-sectional aspect ratio, and masonry compressive strength. The results showed that increasing the FRP layers, corner radius, and FRP jacket stiffness significantly enhanced the axial capacity of the FRP-confined RMCs. However, the increase in the masonry compressive strength and cross-sectional aspect ratio negatively affected the axial capacity gain ratio of FRP-strengthened RMCs.

The phase composition characteristics of AlCoCrFeNi high entropy alloy heat-treated by simple normalizing treatment and its effects on mechanical properties

The AlCoCrFeNi high entropy alloy (HEA) has been regarded as a potential candidate for refractory material due to its uniqueness, and its brittleness can be tuned by heat treatment. In this work, we propose a new heat treatment process to tailor the phases of AlCoCrFeNi HEA, and reach the optimum trade-off of strength and ductility. The results show that normalizing treatment in air can be used to instead of quenching in water to obtain the same phase composition and even better performance of AlCoCrFeNi HEA, then avoiding the shortcomings of quenching, reducing production costs, improving production efficiency and expanding its application prospects. The detailed phase compositions and required temperature of normalizing treatment are B2 + BCC (as-cast) → B2 + BCC + little FCC + little σ (700 °C) → B2 + BCC + FCC + σ (900 °C) → B2 + BCC + little FCC (1100 °C) → B2 + BCC (1300 °C). The 1100 °C treated alloy has the highest ultimate compressive strength (3429 MPa) and compression ratio (33.6 %), and reaches the best strength-ductility trade-off due to its special phase composition and microstructure.

Toughness, Reinforcing Mechanism, and Durability of Hybrid Steel Fiber Reinforced Sulfoaluminate Cement Composites

As a low-carbon ecological cement-based material, SAC (sulfoaluminate cement) has become a research hotspot. This study developed a SAC-based high-performance concrete material with good durability and high toughness. The mechanical properties of different scales of MSF (macro steel fiber) and mSF (micro steel fiber) reinforced sulfoaluminate cement-based composites were mainly studied, including their compressive strength, flexural strength, toughness index, and toughness ratio, and their resistance to sulfate erosion was characterized. The results show that adding MSF and HSF (hybrid steel fibers) can significantly improve concrete’s compressive and flexural strength compared with the Plain group. The compressive strength of SSF1 (1% MSF) and SSF2 (1.5% MSF) increased by 10.9%, 19.6%, and the compressive strength of HSF1 (0.1% mSF, 1.4% MSF), HSF2 (0.2% mSF, 1.3%MSF), HSF3 (0.3% mSF, 1.2% MSF), and HSF4 (0.5% mSF, 1.0% MSF) increased by 23.9%, 33.7%, 37.0%, 29.3%, respectively, while the flexural strength of HSF1, HSF2, HSF3, and HSF4 groups increased by 51.4%, 84.9%, 88.1%, and 64.2%. Compared with the single steel fiber (SSF) group, the HSF group has higher initial crack strength, equivalent flexural strength, toughness index, and toughness ratio. Hybrid fibers have a higher synergistic effect when mSF content is 0.2–0.3% and MSF content is 1.2–1.3%. The mechanism of multi-scale reinforcement of hybrid-steel-fiber-enhanced sulfoaluminate cement-based composites was researched. MSF bridges macro-cracks, mSF bridges micro-cracks, and these two different scales of steel fibers, through filling, bridging, anchoring, pulling off, and pulling out, improve the toughness of composite materials. The mechanism of sulfate corrosion resistance of sulfoaluminate cement-based composites was obtained. SO42− entered the matrix and reacted and formed AFt, filling the matrix’s pores. The whole process is similar to the self-healing process of concrete.

Compressive performance of steel-reinforced concrete columns after exposure to high temperature

Steel-reinforced concrete (SRC) columns have been extensively employed in high-rise buildings due to their superior mechanical properties, especially under fire conditions. In most cases, the fire damaged SRC columns may still be able to re-use after proper repairs. Thus, it is important and essential to investigate the residual behaviors of these post-fire SRC columns. In this study, a total of 75 SRC columns, including 60 that are heated and 15 that are unheated for comparison, are tested under axial compression. Four parameters, including the steel section ratio, the concrete strength, the sectional aspect ratio and the heating duration, are considered to examine their effects on the failure modes, bearing capacities, deformation, axial stiffness and ductility characteristics. It is demonstrated that the strength of SRC stub columns on average decreases by 13%, 20%, 25% and 37% after exposure to high temperature with durations of 30min, 60min, 90min and 120min. Increasing the steel section ratio can effectively decrease the strength loss resulted from heat exposure. While the concrete compressive strength and sectional aspect ratio exhibit little effect on the residual strength. To this end, equations for estimating the ultimate strength of SRC stub columns after exposure to fire are developed via tests. It is verified that the calculation results agree well with the experimental results.

Reduction, stabilization, and solidification of Cr(VI) in contaminated soils with a sustainable by-product-based binder

This study evaluated the use of a sustainable GFD binder for the stabilization/solidification (S/S) of chromium VI (Cr(VI))-contaminated soil. The GFD binder was composed of ground granulated blast furnace slag (GGBFS), fly ash and desulfurization ash, named after the initials of the three materials. The effects of curing time and binder dosage on soil unconfined compressive strength (UCS), Cr leachability, soil pH, and reduction ratio of Cr (VI) were tested. The immobilization mechanisms of Cr(VI) in contaminated soil were further explored using X-ray diffraction (XRD), scanning electron microscopy (SEM), and sequential extraction procedure (SEP). The results showed that the UCS and pH of the soil increased substantially after the GFD binder was added. After 28 days of curing with a 20% binder dosage, the leached total Cr concentration decreased from 34.4 mg/L in the contaminated soil to 1.44 mg/L in the treated soil, and the leached Cr(VI) concentration decreased from 28.0 mg/L to 0.45 mg/L. A Cr(VI) reduction ratio of 96.2% was achieved, indicating the strong reducibility of GGBFS. XRD revealed that the main hydration products of the GFD binder were hydrated calcium silicate (C–S–H) and ettringite. SEM results showed that the formation of hydration products and Cr-bearing precipitates filled the soil pores, resulting in a dense soil structure. The SEP results demonstrated that the levels of the unstable fraction F1 decreased considerably, and that the levels of the stable fractions F3 and F5 increased after treatment. Encapsulation by C–S–H, reduction by sulfides, adsorption of C–S–H, and precipitation of Cr-bearing hydroxides were the main mechanisms involved in Cr immobilization using the GFD binder.

Preparation and Hydration Mechanism of Al-F Complex Alkali-Free Accelerator by Waste Acid of Titanium Dioxide

The objective of this study is to prepare Al-F complex alkali-free accelerator from waste acid of titanium dioxide and to evaluate the hydration mechanism of F-ion complex. Setting time, stability, pH value, 1d compressive strength, 28d ratio of compressive strength and SEM were performed on cement pastes produced with an alkali-free accelerator (aluminum sulfate solution containing F-ion). Results showed that the addition of F-ion could form β -AlF3•3H2O complex, which improved the content of Al3+ ion and the stability of the system. The Al-F complex alkali-free accelerator contributed to the rapid formation of ettringite with network structure, as well as to a faster rate of cement dissolution and hydration. Moreover, a conceptual hydration model for pastes containing F-ion alkali-free accelerator was proposed. F-ion was beneficial to destroy the covering effect of C-H-S gel and form a continuous hydration. According to the results, variations in cement different setting time and mechanical strength caused by different concentration of F-ion in the alkali free accelerator are explained.

Technogenic Fiber Wastes for Optimizing Concrete.

A promising method of obtaining mineral fiber fillers for dry building mixtures is the processing of waste that comes from the production of technogenic fibrous materials (TFM). The novelty of the work lies in the fact that, for the first time, basalt production wastes were studied not only as reinforcing components, but also as binder ones involved in concrete structure formation. The purpose of the article is to study the physical and mechanical properties of waste technogenic fibrous materials as additives for optimizing the composition of raw concrete mixes. To assess the possibility of using wastes from the complex processing of TFM that were ground for 5 and 10 min as an active mineral additive to concrete, their chemical, mineralogical, and granulometric compositions, as well as the microstructure and physical and mechanical characteristics of the created concretes, were studied. It is established that the grinding of TFM for 10 min leads to the grinding of not only fibers, but also pellets, the fragments of which are noticeable in the total mass of the substance. The presence of quartz in the amorphous phase of TFM makes it possible to synthesize low-basic calcium silicate hydrates in a targeted manner. At 90 days age, at 10–20% of the content of TFM, the strength indicators increase (above 40 MPa), and at 30% of the additive content, they approach the values of the control composition without additives (above 35 MPa). For all ages, the ratio of flexural and compressive strengths is at the level of 0.2, which characterizes a high reinforcing effect. Analysis of the results suggests the possibility of using waste milled for 10 min as an active mineral additive, as well as to give better formability to the mixture and its micro-reinforcement to obtain fiber-reinforced concrete.

Accelerated carbonation of regenerated cementitious materials from waste concrete for CO2 sequestration

Regenerated cementitious materials (RCM) was peeled sufficiently from the surface of aggregate after waste concrete subjected to air cooling after heating at 400 °C and 650 °C and then RCM was utilized to prepare carbonated products by accelerated carbonation for CO2 sequestration. In this study, the effect of the compaction rate of compacted RCM and water-solids ratio (w/s) on the CO2 uptake and mechanical properties of carbonated RCM (C-RCM) was evaluated and the carbon footprint of RCM was assessed. Results indicate the CO2 uptake and compressive strength of C-RCM subjected to 650 °C (C-RCM 650) are higher than that of C-RCM subjected to 400 °C (C-RCM 400) for the higher carbonation activity, larger porosity of compact and lower voids between RCM particles. In consideration of the carbon emissions from the calcination process, the net CO2 uptake of C-RCM 650 is similar to that of C-RCM 400 and carbonated hydrated cement paste prepared at room temperature. However, the ratio of compressive strength to CO2 uptake of C-RCM 650 is far more than that of C-RCM 400 and carbonated hydrated cement paste, which shows a better overall performance.

Correlation between the tensile to compressive strength ratio and mechanical parameters of rock based on a nonlinear M-C criterion

Correlation between the tensile to compressive strength ratio and mechanical parameters of rock based on a nonlinear M-C criterion