28-day Compressive Strength Research Articles

Environmental, economic and engineering performances of aqueous carbonated steel slag powders as alternative material in cement pastes: Influence of particle size

The low reactivity and volume expansion issue of steel slag limits its application as alternative to cement. Studies demonstrated that aqueous carbonation (AC) can enhance the cementitious properties of finely sized steel slag as a cementitious supplementary material (SCM). However, the impact of particle size on the CO2 uptake capacity and its association of performance of carbonated steel slag remains unexplored. This study aims to optimize the grinding levels by examining the fineness of the steel slag used as SCM to reduce the high-energy consumption while maintaining the CO2 sequestration and properties of SCM. The results show that reducing the size of steel slag is favorable for CO2 sequestration (particle size 22.4–112.6 μm corresponds to sequestration of ∼88.5–37.9 kg CO2/t steel slag) and improve the leaching of Mg ions for mineralization. The life cycle assessment shows that the global warming potential of AC of steel slag is ∼96.2–24.9 kg CO2-eq/t steel slag, which can offset the carbon emissions due to further grinding. The 28-day compressive strength of the cement pastes blended with finer carbonated steel slag was also relatively higher due to the formation of mono-carboaluminates and stabilization of ettringite in facilitating the bond strength between the carbonated steel slag particle and the cement paste matrix. According to 3E (engineering, environmental and economic) triangle model, 22.4 μm steel slag powder showed the best comprehensive performance, including an increased revenue of 40.8 CNY/ton steel slag.

Prediction of high-temperature creep in concrete using supervised machine learning algorithms

In this paper, supervised machine learning techniques were employed to develop a prediction model for concrete creep at elevated temperatures. Several algorithms were considered including artificial neural networks (ANN), decision tree regression (DTR), random forest regression, linear regression and Gaussian process regression (GPR) models. A dataset of short-term, basic creep was compiled from experimental data reported in the literature for algorithm training. The selected input variables were time, temperature, 28-day compressive strength, compressive stress, fine and coarse aggregate mass, and steel and PP fiber mass. The data was split into training and verification sets, with 70% used for model training and the remaining 30% for model verification. The results demonstrate that ANN, DTR, RFR and GPR models can accurately reflect concrete creep behavior at elevated temperatures based on statistical indicators. However, further analysis showed that the GPR was the best-performing model, providing highly accurate representations of creep behaviour and demonstrating superior performance to existing empirical equations. Conversely, the DTR was found to not accurately reflect experimental data. Additionally, a Shapley additive explanation analysis was conducted that assessed the significance of each input parameter on model prediction. This research highlights the potential of machine learning techniques to accurately model high -temperature concrete creep behavior and thus represents a powerful tool for engineers and researchers.

Early estimation of 28-day compressive strength of mortars using regression and neural network-based models

Concrete, the most commonly used construction material, presents a challenge in determining its compressive strength (CS) after 28 days of manufacture. This study aims to predict the compressive strength of conventionally cured (CC) mortar specimens using data from accelerated microwave-cured (MC) specimens. Two hundred and seventy-six specimens with different mixes and admixtures were divided into two groups: one half was subjected to MC and the other to CC. The CSs of the CC specimens were determined after 28 days, while the MC specimens were subjected to additional tests such as ultrasonics pulse velocity and three-point bending after microwave curing. Regression and artificial neural network models (ANN) were developed using the obtained data. While the data of the specimens subjected to MC were used as independent variables of the developed models, the compressive strength of the conventionally cured specimens (CC) was used as the dependent variable. In the models, 60% of the data were used for training, 20% for validation, and 20% for testing. The predictive capabilities of the developed models were compared using performance statistics such as root mean square error (RMSE), root mean absolute error (MAE), and Nash-Sutcliffe efficiency coefficient (NSE). As a result of the study, it was found that compared to all models, the highest performance values were obtained by the ANN-based models. Among the regression-based models, the multivariate adaptive regression splines method (MARS) obtained the highest performance values. Considering the calculated NSE values, it was determined that the ANN-based model gave similar results to the MARS model for the training and validation data sets but provided performance values approximately 25% higher than the MARS model for the test data set. In addition, the results obtained from the modeling studies showed that the CSs of concrete could be predicted very accurately and well in advance.

Prediction of compressive strength of cementitious grouts for semi-flexible pavement application using machine learning approach

This study involves the preparation of cement grout samples by varying proportions of superplasticizer (SP) and water-cement (w/c) ratio (0.25–0.45) which were tested for computing flow value and 1-day, 7-day, and 28-day compressive strength. With 75 data points a neural network model was developed to predict the 28-day compressive strength based on w/c ratio, superplasticizer percentage, flow value, and compressive strengths of 1-day and 7-day as input variables. Due to the better performance of Artificial Neural Networks (ANN) over other applied models, this study predicts a confident pattern of relationship between w/c ratio (indirect), superplasticizer (direct up to 3%), and the corresponding strength characteristics of the study samples. The prediction power of the developed model has been improved from R2 = 0.959 to R2 = 0.984 by optimizing the number of neurons, activation function, and optimizer. The best performance was observed in the case of Model45-R_A. The same model was used for assessing the effect of the percentage of superplasticizer and water cement ratio on 28 days compressive strength where the compressive strength of 73.941 MPa was recorded in the case of 3% superplasticizer and w/c of 0.25.

Predicting the 28-day compressive strength by mix proportions: Insights from a large number of observations of industrially produced concrete

Many previous studies explored machine learning (ML) models to predict the 28-day compressive strength (f28) by the mix proportions using laboratory data, but only a few exploited industrial data. Predicting industrial concrete performance by laboratory models could be questionable as an industrial environment involves much more uncertainties. This study has applied ML models on 12,107 observations of industrially produced concrete that are associated with a wide range of concrete applications of various strength and slump requirements. A systematic approach has been taken to develop seven ML models to predict f28, covering data visualization, model selection and assessment, model finalization, and variable importance analysis. Significant improvements have been achieved compared to previous studies using field concrete data. It is also found that the industrial data has a multimodal problem and is much noisier than laboratory data. The outcomes of this study can serve as a useful reference in predicting f28 and designing the mix to produce the desired concrete in an industrial environment.

Relationship between fractal characteristics of pore-structure and thermal properties of FA-based AAM under different curing conditions

The microstructure of hardened alkali-activated materials (AAM) plays an essential role in determining the mechanical properties at elevated temperatures, particularly the pore structure. Mercury Intrusion Porosimeter (MIP) was employed to study the fractal characteristics of the pore structure of samples under standard and sealed curing conditions, which includes pore size distribution, shape, surface area, and tortuosity of AAM pastes after exposure to high temperatures. Additionally, the compressive strength of AAMs at elevated temperatures was determined. Comparing the samples under standard curing conditions, sealed curing conditions significantly improved the 28-day compressive strength (43.6 MPa) and residual compressive strength (achieving 60.2% of the 28-day strength) when exposed to 1000 °C. Based on research, the fractal characteristics of pore structures have a significant effect on the thermal properties of samples at high temperatures. Differences in thermal properties may be attributable to resistance caused by pore structures with heterogeneity and complexity, as well as the shape of the pores, which have small pore throats and large pore capacities. Under standard curing conditions, the samples exhibited a pore structure characterized by a reduced neck diameter, larger cavity size, a coarser pore surface, and decreased connectivity. As a result, the 28-day samples under standard curing conditions experienced significantly elevated pore pressure.

Behavior of Reinforced Composite Foamed-Normal Concrete Beams

A study has been undertaken to investigate the production and behavior of beams made with foamed, normal, and composite concrete and reinforced with different steel percentages (under, balanced, and over). Nine reinforcement beams, including three normal-weight concrete, three lightweight foamed concrete, and three composite concrete, were made with similar rectangular cross sections of dimensions (150 × 250 mm) and length of 1500 mm. A 28-day compressive strength of 29 MPa (suitable for structural purposes) was achieved for all investigated concrete mixes. Ultimate load, crack mode, ductility, deflection, and stiffness as flexural parameters were investigated. The results showed that in terms of loading, the load of composite concrete beams was equal to that of normal concrete beams, and a slight increase in the lightweight foamed concrete beams was noticed. The ductility of foamed concrete beams with balanced reinforcement and under reinforcing was lower than that of normal concrete. In the case of the over-reinforcement beams, the ductility of foamed concrete beam increased by about 19.5% compared to that of normal reinforced concrete. In addition, the ductility and stiffness of composite concrete beams increased by about 91.7% and 5.6% compared to normal beams and 61% and 15.1% compared to foamed concrete beams, respectively.

Predicting the Twenty-Eight Day Compressive Strength of OPC- and PPC-Prepared Concrete through Hybrid GA-XGB Model

This research set out to create a computational tool for predicting the 28-day compressive strength (CS) of concrete prepared from ordinary Portland cement (OPC) and Portland pozzolana cement (PPC) cement. 1,062 datasets of concrete were collected from laboratory experiments. From 1,062 datasets, 524 samples belonged to OPC and 538 samples belonged to PPC. eXtreme gradient boosting (XGBoost) algorithm optimized with genetic algorithm (GA) was utilized for developing an efficient model. The R value obtained for GA-XGBOPC and GA-XGBPPC models in training (TR) and testing (TS) dataset are almost ≥0.90. Mean absolute error (MAE) and root mean square error (RMSE) values obtained for the GA-XGBOPC model were 2.155 and 2.923, respectively. Similarly, the values for the GA-XGBPPC model were 1.815 and 2.888, respectively. The developed models were found to predict more than 90% of the observations within ±20% variations. The level-1 and level-2 validation results certify the GA-XGBOPC and GA-XGBPPC models’ generalizability. Ultimately, a user-friendly laborless and financially feasible computer software or tool was generated in Python for assistance to the field and design engineers in estimating the CS of concrete.

Investigating the effects of stabilization carried out using fly ash and polypropylene fiber on the properties of highway clay soils

Improving highway subgrades is the most crucial step that increases the performance and longtime durability of pavements. Using fly ash to improve the properties of subgrades and synthetic fibers as additives to increase their strength in recent years is an effective method. It is essential to determine how fly ashes affect the strength properties of subgrade soils in the long term with a time-dependent curing effect and how synthetic fibers affect the strength properties of subgrade soils, especially in the short term before curing. Furthermore, another vital issue is determining the extent to which freeze–thaw cycles that occur during winter months due to regional climatic conditions reduce the strength of the subgrade soils. For this purpose, a regional high-plasticity soil representing the problematic subgrade was reinforced with fly ash at different percentages (10%, 20%, 30% and 40%), and a series of experiments were carried out to determine the plasticity, compressibility and strength properties of these soil mixtures. Besides the clayey soil and fly ash, the microstructures of these mixtures were also examined by XRF, XRD spectrometry, FT-IR spectroscopy and SEM analyses and the relationships between mechanical behavior and microstructure were tried to be explained. Furthermore, the impact of polypropylene fibers added to the soil at 0.5% of the dry mass and freeze–thaw cycles on the strength of the subgrade soils was determined. The results showed that the effective fly ash mixture ratio for stabilization with fly ash was 10%, and when the 28-day unconfined compressive strengths of the fly ash mixture and the natural soil were compared, the fly ash mixture increased the strength by 85.8%. Furthermore, the fiber additives were determined to increase the shear strength at ratios ranging from 3.0% to 21.0% and that approximately 80% strength loss occurred in the natural soil due to freeze–thaw cycles, but fly ash and synthetic fiber additives can increase the strength by compensating for the strength loss caused by freeze–thaw cycles.

Performance of self-compacting concrete cast in hot weather conditions

This work focused on how self-compacting concrete (SCC) performs in situ in hot weather conditions at an ambient temperature of about 35°C. Tests for the rheological properties and compressive and splitting tensile strength aspects were carried out. The results of SCC mix ingredients on the rheological and hardened features of SCC mix were studied. Variations in the amount of portland cement content (CC), water to cement ratio (w/c), coarse to fine aggregate ratio (C : F), chemical admixture ratio, and pozzolanic admixture ratio were considered. Optimum values were obtained for these ingredients, which satisfied the SCC rheological characteristics and gave a 28-day compressive strength of 42 MPa, and 52 MPa after 28 days and 56 days, respectively. These optimum constituent values were 450 kg·m–3 of cement, 0.45 water cementitious ratio, and a coarse to fine material ratio of 1 : 0.8, a high range superplasticizer of 2%, and a mineral admixture of either 5% silica fume or 25% fly ash as a substitute for a similar amount cement.

The Influence of Fiber on the Mechanical Properties of Controllable Low-Strength Materials.

Numerous studies have been conducted on fiber-reinforced concrete; however, comparative investigations specifically focusing on the utilization of fibers in CLSM remain limited. In this study, we conducted a systematic investigation into the mechanical properties of controlled low-strength material (CLSM) by manipulating the length and doping amount of fibers as control variables. The 7-day compressive strength (7d-UCS), 28-day compressive strength (28d-UCS), and 28-day splitting strength of CLSM were employed as indicators to evaluate the material's performance. Based on our comprehensive analysis, the following conclusions were drawn: (1) A positive correlation was observed between fiber length and material strength within the range of 0-6 mm, while conversely, a negative correlation was evident. Similarly, when the fiber doping was within the range of 0-0.3%, a positive correlation was identified between material strength and fiber doping. However, the strength of CLSM decreased when fiber doping exceeded 0.3%. (2) SEM and PCAS analyses provided further confirmation that the incorporation of fibers effectively reduced the porosity of the material by filling internal pores and interacting with hydration products, thereby forming a mesh structure. Overall, this study offers valuable insights into the manipulation of fiber length and doping amount to optimize the mechanical properties of CLSM. The findings have important implications for the practical application of CLSM, particularly in terms of enhancing its strength through fiber incorporation.

Carbon nanofibers and polyvinyl-alcohol fiber hybrid-reinforced high-performance concrete: Mechanical property, chloride penetration resistance, and material characterization

The hybridization of nanomaterials and macroscopic fibers is currently a popular topic. The aim of this study was to explore the application potential of incorporating carbon nanofibers (CNFs) into concrete and to analyze the effect of CNFs dispersant on concrete slump and early strength. Polyvinyl alcohol (PVA) fibers and CNFs were used to prepare composite fiber-reinforced (CNFs-PVA) concrete to improve the continuity of concrete properties at the micron/nanometer scale. The engineering properties such as compressive strength, flexural strength and resistance to chloride ion erosion performance of the concrete were investigated, and the microstructure of concrete was characterized using X-ray diffraction (XRD), scanning-electron microscopy (SEM), and X-ray computed tomography (X-CT). The results showed that CNFs could improve the early strength. The combined use of CNFs and PVA increased the 28-day compressive and flexural strength by 23.38% and 28.73%, respectively, compared to the control group. Correspondingly, the electric flux and Migration rate of chloride ions (DRCM) were minimized. From the SEM and XRD test results, it is clear that CNFs and PVA fibers can: (i) bridge low-density C-S-H to form higher-density C-S-H gels, (ii) form longer chain-like fibers with enhanced load transfer and chloride binding capacity, (iii) act as internal curing agents to enhance hydration at the interface, (iv) promote the formation of the aluminum phase hydration products and calcium carbonate phase, and (v) CNFs and PVA refine the pore size by increasing the gel pores and reducing the percentage of microcracks. The combined results indicate that the improved performance of CNFs-PVA is due to the combined effect of bridging and nucleation of hydration products by CNFs, adsorption of hydration products by CNFs-PVA, and promotion of pore filling by the generated hydrides such as calcium carbonate and ettringite. These findings provide new insights for the design of high-performance concrete materials.

Self-compacting concrete produced with recycled concrete aggregate coated by a polymer-based agent: A case study

Understanding the effects of recycled concrete aggregate (RCA) and polymer impregnation on the properties of self-compacting concrete (SCC) is crucial for the construction industry's efforts to reduce environmental impact and utilise recycled materials. This study aims to examine the impact of RCA inclusion and polymer impregnation on the properties of SCC, in response to the urgent demand for sustainable construction practices. Two different methods of polymer impregnation were evaluated to assess their impact on the workability and hardened characteristics of SCC. The SCC mixtures were prepared using river sand (natural fine aggregate (NFA)), natural crushed limestone (natural coarse aggregate (NCA)) and a polymer impregnation level of 0.05 wt% of the water content, with a water-to-cement ratio of 0.34. RCA was used as a complete replacement for NFA and NCA, adhering to the American Society for Testing and Materials (ASTM) C33 standards for recycled fine concrete aggregate (RFCA) and recycled coarse concrete aggregate (RCCA)The workability of the SCC mixtures was evaluated based on the criteria set by the European Federation of National Associations Representing for Concrete (EFNARC). Among the hardened properties, the compressive strength of the hardened properties was tested at four different time intervals (1, 3, 7 and 28 days), and the integrity of the SCC specimens was assessed using ultrasonic pulse velocity. The polymer impregnation process resulted in a slower compressive strength development rate compared to that observed in the control concrete. However, combining polymer impregnation type 1 with either RFCA and NCA or RCCA and NFA significantly increased the 28-day compressive strength by 5.02% and 1.80%, respectively. These findings provide valuable insights into the behaviour of SCC incorporating RCA and polymer impregnation. Optimising the selection and combination of materials can enhance the performance and sustainability of SCC in construction applications.

Evaluation of Fluidity and Strength of High-Early-Strength Cement-Based Repair Materials by Adding SB Latex and Wollastonite Mineral Fibers.

Concrete structures often fail to perform their original functions due to problems such as deterioration and damage over time. Therefore, various repair materials have been studied to maintain deteriorated concrete structures. This study experimentally investigated the mechanical properties of high-early-strength cement-based repair materials for spraying. For spraying, the cement-based materials should have adoptable fluidity and strength: 200 ± 100 mm for flow; 20 MPa at 24 h and 40 MPa at 28 days for compressive strength, and 8 MPa at 28 days for flexural strength. Wollastonite mineral fibers (3-5 wt.%) and styrene-butadiene (SB) latex (5-7 wt.%) were studied to enhance this requirement. Fluidity was evaluated by flow test and measuring the heat of hydration; mechanical properties were evaluated in terms of compressive and flexural strength. The cement-to-silica sand ratio (C:S ratio) was also applied differently to adjust the pot life of polymer cement-based material (1:1 and 1:1.5) as a binder. Because wollastonite mineral fibers and SB latex affect workability, the water-to-binder ratio was regulated to reach the target flow according to the amount of wollastonite mineral fibers and SB latex. Regardless of the C:S ratio, all studied mixtures met the target 28 day compressive strength at 24 h, decreasing in strength with increasing amounts of wollastonite mineral fibers and latex. Flexural strength also fulfilled the target value, and it increased with increasing amounts of wollastonite mineral fibers and latex, unlike compressive strength. The optimal mix proportion of high-early-strength cement-based repair materials constituted 3 wt.% wollastonite mineral fibers and 5 wt.% SB latex as the binder in a C:S ratio of 1:1.5.

Disparity in research findings on parent concrete strength effects on recycled aggregate quality as a challenge in aggregate recycling

Although the idea behind recycled concrete aggregates (RCA) is not particularly novel, its potential for reuse must be verified by carefully evaluating the properties of RCA produced from various sources. Previous research has demonstrated that the mechanical qualities of the parent concrete (PC), which may originate from a number of sources, can have a substantial impact on the characteristics of RCAs. But the conclusions of these literary works were inconsistent. Researchers and construction stakeholders in regions where there have been few or no studies on the topic such as Ethiopia may find it challenging to choose which of these concepts to use in their practical applications as a result of these comparable contradictions in the literature. Therefore, this research conducted new physical and mechanical property tests on recycled aggregates derived from various strengths of parent concrete laboratory cubes and concrete remains found from demolished buildings in Ethiopia in an effort to explain the considerable range of variation in results in the literature and to investigate the aspects of recycled aggregates that have not yet been explored. Parent concretes with 28-day cube compressive strengths of 25, 37, 45, and 67 MPa were produced in the laboratory, and demolished concrete from real-life structures aged 5 and 23 years with cube compressive strengths of 25 and 37 MPa, respectively, was utilized. The study's findings showed that the qualities of recycled aggregates were favorably associated with an increase in the strength of parent concrete. Recycled concrete aggregates' resistance to abrasion, impact, and crushing resistance, specific gravity, and water absorption all improved with an increase in the strength of parent concrete, although mortar content climbed. As a result, it is anticipated that this research will assist researchers and construction stakeholders in better understanding how recycled aggregate properties are impacted by variations in parent concrete strength.

Study on the mechanical and microscopic properties of steel fiber reinforced reactive powder concrete under different curing methods

In order to investigate the effects of different curing regimes on the mechanical properties and hydration products of micro steel fiber (MSF) reinforced reactive powder concrete (RPC), three curing methods were selected: spraying curing (SPC), standard curing (SC) and (90 °C hot water + spray) curing (H + SPC). The variation rules of MSF content and age on the compressive and splitting tensile strength of RPC were analyzed, and the MSF strengthening mechanism and microscopic morphology were studied using scanning electron microscopy and X-ray diffraction microscopy techniques. Prediction models were subsequently developed for 28-day compressive and splitting tensile strength of micro steel fiber reinforced reactive powder concrete (MSF-RPC). The experimental results showed that the mechanical properties of RPC were significantly improved due to the incorporation of MSF. Under the three curing regimes, the optimal fiber volume content of MSF-RPC was 1.65%, with the improvement rates in 28-day compressive strength of MSF-RPC under SPC, SC, and H + SPC to be 33.38%, 32.22%, and 30.65%, respectively, compared with that of plain RPC. The corresponding improvement rates in splitting tensile strength were 236.24%, 211.29%, and 238.66%. The strength obtained under H + SPC was slightly higher than that obtained under SC, while its later growth rate was lower than that obtained under SC or SPC. Although the strength obtained under SPC was slightly lower than that obtained under SC, the engineering requirements were basically met, and SPC can be easily promoted in engineering practice.

Study of Aerated Lightweight Mortar Using Aluminium Powder and Local Materials

Conventional burnt clay bricks are still mostly used as building materials for both load-bearing and non-load-bearing walls in Nepal. The use of brick walls not only increases the dead loads on the structures but also becomes the main cause of casualties during the earthquake. This paper describes the development of an alternative lightweight mortar using aluminium powder to replace the bricks. The base mixture of the mortar was experimentally determined and the properties were studied with the ranging content of the aluminium powder by weight of cement. The result showed a decrease in the density and compressive strength but an increase in the water absorption while increasing aluminium powder content. The density was possible to decrease by about 52% with the use of 0.9% aluminium powder. The decrease was very less while increasing the aluminium content from 0.6% to 0.9%. The 28-day compressive strength was decreased by 59% and 63% at aluminium content of 0.6% and 0.9% respectively. With the achievement of a density of less than 1000 kg/m3 and a 28-day compressive strength of more than 7.5 MPa, the optimum content of the aluminium powder was 0.6%. The implementation of this result implies producing lightweight bricks, blocks and panels replacing the burnt clay bricks. It not only lightens the building structures and avoids the casualties during big earthquakes but also saves the environment by minimizing the carbon-di-oxide, avoids the degrading of agricultural soils and even minimizes the risk of climate change.

Effects of different nanomaterials on the early performance of ultra-high performance concrete (UHPC): C–S–H seeds and nano-silica

The early hydration of UHPC can be retarded by the low water/binder ratio, the high polycarboxylate superplasticizers dosage, and the large supplementary cementitious materials (SCM) content. In this study, the effects of the prepared nanoscale C–S–H seeds and nano-silica (NS) on the early performance of UHPC were compared. The mechanism of nanomaterials influencing the early hydration of UHPC was further characterized by calorimetry, thermal analysis, nuclear magnetic resonance (NMR), and mercury intrusion porosimetry. The results showed that the 1-day compressive strength of UHPC samples with 0.3 wt% C–S–H seeds and NS increased by 457% and 25% respectively compared to the control sample. Compared to NS, C–S–H seeds were more effective in accelerating the early (before 3 d) hydration to produce hydrates and refine the pore structure of UHPC. The NMR results further implied that compared with the NS, the C–S–H seeds was 12% and 343% more efficient in accelerating the early hydration of cement and SCMs, respectively. However, the performance enhancement of nanomaterials was effective at 1 d and had little effect thereafter.

Fire-resistant and Thermal Insulation Improvements of Cement Mortar with Auto Glass Waste Sand

This research investigates the physical, mechanical, thermal conductivity, and fire-resistant properties of mortar incorporating with auto glass waste (AGW). The crushed AGW was used as fine aggregate to substitute natural sand (NS) from 0 to 100% by volume. The 40% replacement with AGW was optimum, with a slight increase in the 28-day compressive strength. The 90-day compressive strength of 100% AGW increased by 33% compared to NS mortar (without AGW) due to the increased pozzolanic reaction. The replacement of sand with AGW resulted in improvements in thermal insulation properties and fire resistance of mortars. The 100% replacement with AGW decreased the thermal conductivity coefficient by 63%, while the density decreased by only 2.8% compared to the NS mortar. The residual compressive strength increased with incorporating AGW after exposure to elevated temperatures. The 100% replacements with AGW showed a maximum compressive residual mortar strength of 66 MPa (126%) after exposure to high temperatures at 300°C.

CO2 Curing of Reactive Powder Concretes Modified by Waste Limestone Powder

Incorporating waste stone powders into the production of reactive powder concretes (RPCs) can be eco-friendly. Since high cementitious material content is used in producing RPCs, CO2, as a harmful greenhouse gas, was used for carbonation curing in this study. For this purpose, waste limestone powder was substituted by 0%, 18%, 36% and 54% of silica sand and the specimens were cured in water for up to 90 days in a CO2 chamber for up to 48 hours. The physical and mechanical properties of the concrete and the specimens' CO2 uptake were measured at different ages. Results showed that the 28-day compressive strength of the moist cured RPCs was higher than 100 MPa and the properties of the RPCs were improved by increasing limestone substitution. CO2 curing of the RPCs significantly increased the samples' compressive strength and limestone-powder substitution as silica sand significantly decreased the carbonation and autogenous shrinkages of the RPCs. Moreover, carbonation curing can make eco-friendly limestone-modified RPCs, where their properties are improved. KEYWORDS: CO2 curing, Reactive powder concrete, Waste limestone powder, Shrinkage.