Prism Compressive Strength Research Articles

Mechanical properties of reactive powder concrete under compression at ultra-low temperatures

In this paper, the mechanical properties of reactive powder concrete (RPC) at ultra-low temperatures were studied. RPC prisms (300 mm × 100 mm × 100 mm) were tested at ultra-low temperatures (20 °C, 0 °C, −20 °C, −40 °C, −80 °C, −120 °C, −165 °C) and resulting prism compressive strength, compressive stress-strain curve, and toughness were determined. The increase in prismatic compressive strength of RPC at ultra-low temperatures is greater than that of ordinary concrete, with an overall strength of about 2.12 times that of ordinary concrete. Pore water freezing behavior was also studied to assess the effects on the mechanical properties of RPC in ultra-low temperatures. The water-ice phase transition further improved the RPC strength. With the reduction in temperature, The change in elastic modulus of RPC change is small, the peak strain of specimens at different temperatures increases with the decrease in temperature. The peak strain of RPC showed an overall linear increase with decreasing temperatures, and the water-ice phase transition at negative temperature increases the peak strain of RPC, adding steel fibers improves the RPC ductility, limiting the fracture. With the temperature reduction, RPC toughness first increases and then decreases. The toughness is lowest at room temperature, and highest at −120 °C, which is 2.26 times higher than at room temperature. RPC has better toughness than normal concrete at different temperatures, the reduction of temperature relatively improves the toughness of RPC, and the addition of steel fibers plays a vital role in improving the toughness. This study can serve as technical support for using RPC to design liquefied natural gas full-capacity tanks.

Fragility functions for masonry infill walls in RC frames with the in-plane and out-of-plane loading

This paper presents a comprehensive analysis of masonry infill walls under both in-plane and out-of-plane loading, offering limit state criteria and fragility functions. Four distinct damage states are defined to capture damage evolution under diverse loading conditions. The research establishes a thorough database documenting in-plane and out-of-plane drift levels corresponding to each damage state, derived from experimental testing on masonry-infilled frame specimens from existing literature. Fragility functions were developed based on in-plane or out-of-plane drifts for four distinct damage states. The study systematically evaluates the influences of masonry prism compressive strength, slenderness ratio, and aspect ratio. Notably, the impact of prior in-plane damage on out-of-plane vulnerabilities is investigated. The study introduces equations designed to predict changes in the central tendency and dispersion parameters of out-of-plane drift thresholds, accounting for variations in prior in-plane drift ratios. It’s crucial to highlight that the empirical fragility functions proposed in this study are exclusively based on experimental tests involving tight-fit single-leaf infill walls without openings or modifications.

Investigating specimen size and shape effects on compressive mechanical behaviors of recycled aggregate concrete using discrete element mesoscale modeling

In comparison to natural aggregate concrete (NAC), recycled aggregate concrete (RAC) typically exhibits a more diverse composition of materials, heightened variability and greater inherent weaknesses. These characteristics may result in varying effects of specimen size and shape on compressive responses. Within this framework, the present study endeavors to comprehensively investigate these influences on RAC's compressive properties and their underlying mechanisms utilizing discrete element simulation technology. At the mesoscale, RAC is depicted by several components, encompassing both new and old aggregates, mortar and interfacial transition zones. Through integrating contacts for each phase, elucidating mesoscale mechanical responses with a parallel bond model and introducing Weibull random fields to delineate variations in phase properties, this study effectively simulates these mechanical responses. Subsequent extensive calculations scrutinize the repercussions of specimen size and shape on the compressive strength, elastic modulus, peak strain and failure modes of RAC across varying water-to-binder ratios. The study concludes that RAC manifests a size effect, albeit less pronounced than in NAC with an equivalent water-to-cement ratio, yet more significant than in mortar. Moreover, owing to end plate constraints, the reduction in RAC's cubic compressive strength is notably less than its prismatic compressive strength. Based on these findings, it is recommended to establish the strength size reduction coefficient and cube-to-cylinder shape coefficient for RAC at 0.86 and 0.72, respectively. Notably, these values diverge significantly from the respective 0.81 and 0.78 coefficients for NAC.

Uniaxial tensile properties of steel fiber-reinforced recycled coarse aggregate shotcrete: Test and constitutive relationship

This paper presents the uniaxial tensile characteristics and stress-strain curves of steel fiber-reinforced recycled coarse aggregate shotcrete (SFRCAS). The study variables include concrete strength grade (C20, C30, and C40), recycled aggregate (RA) replacement ratio rg (0%, 30%, 50%, 70%, and 100%), and steel fiber (SF) volume fraction Vf (0%, 0.5%, 1%, 1.5%, and 2%). The experimental results demonstrate that the uniaxial tensile failure process of SFRCAS can be divided into three stages. The cohesiveness of concrete is improved with an increase in strength grade. However, the ratio of tensile to prismatic compressive strength stays constant at approximately 0.07. Adding Vf from 0% to 2% enhances the restraint of micro-cracking within the concrete by the SF. This leads to a significant increase of up to 120% in the uniaxial tensile strength. Furthermore, the stress-strain curve exhibits improved ductility, enhancing the toughness of SFRCAS. Based on the experimental results, empirical segmented constitutive models of Guo and single-parameter constitutive models of Sargin are fitted for SFRCAS. These constitutive models effectively predict the stress-strain behavior of SFRCAS, and the recommended formulas for model parameter calculation exhibit high accuracy. The research findings are essential for the design and detailed analysis of SFRCAS structures.

Mechanical Properties of Seawater Sea-sand Recycled Concrete in Sulfate Attack Environment

Seawater sea-sand recycled concrete (SSRAC) is a new sort of green concrete, it has good environmental and economic benefits. In this paper, the dry-wet cycle and full immersion erosion environments is simulated. The change characteristics of mechanical properties of SSRAC under sulfate attack are studied and compared with ordinary concrete (OC) and freshwater river sand recycled concrete (RAC). The test shows that compared with immersion erosion, the dry-wet cycle significantly accelerates the deterioration rate of concrete. For the concrete in full immersion condition, the strength is still in the rising stage when the immersion corrosion to 120 d, and there is no obvious change of appearance. In dry-wet cycles, apparent damage gradually extends from the diagonal to the surrounding. The damage deterioration starts from the surface layer and gradually deepens. The prismatic compressive strength and corrosion resistance coefficient of SSRAC show the same law as OC and RAC, which increases first and then decreases. The corrosion resistance coefficient is lower than 75% at 120 cycles. The sulfate resistance of SSRAC is significantly inferior to OC and slightly greater than RAC.

Strength characteristics of lightweight concrete based on granular foam glass ceramics

Introduction. Over the past 20–30 years, a wide range of effective porous aggregates with a high content of glass phase of various types and low-heat-conducting lightweight concretes of various structures based on them has been developed.In recent years, JSC Research Center of Construction has developed a new highly efficient single-stage technology for the production of porous granular foam glass ceramics (UCS). It is based on the production of raw granules by mixing and granulating a highly porous powder of opal-cristobalite rock with a sodium-containing solution. This ensures the maximum area of the interfacial boundary, the most uniform distribution of all components at the micro level and, as a result, ensures glass formation at a temperature that does not exceed the foaming interval of the finished glass phase.The aim of the publication is to study the problems of the features of the strength characteristics of lightweight concrete on granular foam glass ceramics.Materials and methods. The strength of cubes made of light concrete on the UCS under compression (R) was determined on samples with a size of 10 × 10 × 10 cm and 7 × 7 × 7 cm according to State Standard 10180-2012 with an assessment of strength according to State Standard 18105-2018.The prismatic strength coefficient (Kpp) was determined by the results of compression tests of samples-prisms with dimensions of 10 × 10 × 40 cm and 7 × 7 × 28 cm and samples made from the same batch-cubes with dimensions of 10 × 10 × 10 cm and 7 × 7 × 7 cm.Bending tensile strength (Rtb) (Figure 2) and splitting strength (Rtt) were determined, respectively, on 10 × 10 × 40 cm prism samples and 10 × 10 × 10 cm cube samples according to State Standard 10180-2012 with an assessment of strength values according to State Standard 18105-2018.Axial tensile strength (Rtb) and splitting strength (Rtt) were determined, respectively, on prism samples measuring 7 × 7 × 28 cm according to State Standard 10180-2012. The strength of the prisms (prismatic strength, Rb) was determined on samples of prisms 10 × 10 × 40 cm according to State Standard 24452-80.Results. The article presents the results of experimental and theoretical studies of the basic strength properties of thermal insulation and structural-thermal insulation lightweight concrete on granulated foam ceramic (UCS) with a density of 500 to 800 kg/m3, as well as structural lightweight concrete with a density of up to 1700 kg/m3 of optimal compositions (prismatic compressive strength, prismatic strength coefficient, axial tensile strength, tensile strength during bending and splitting).Various dependencies on the evaluation of the experimental data obtained are analyzed and recommendations are given for inclusion in regulatory documents, in particular, in SP 351.1325800.2017 "Concrete and reinforced concrete structures made of light concrete. Design rules".Conclusions. Experimental data have been obtained on a higher prismatic strength coefficient for lightweight concrete at the UCS, which in the future may be the basis for increasing the standard design strength resistance under axial compression for this type of lightweight concrete.The values and formulas for determining the prismatic strength and the prismatic strength coefficient of light concrete of the tested compositions at the UCS can be used in the calculation and design of large-format wall panels of a new type.Experimental and calculated data on the tensile strength of the tested compositions of lightweight concrete of a porous structure at the UCS have been obtained, which can be taken into account when adjusting regulatory documents.When using lightweight concrete of a porous structure on the UCS to increase the shrinkage crack resistance of such concrete for enclosing structures, it is advisable to use dispersed reinforcement with polymer fiber, which also increases the heat-protective properties of such structures. The article presents the results of studies of the main strength properties of thermal insulation and structural-thermal insulation lightweight concretes on the UCS with a density of 500 to 800 kg/m3, as well as structural lightweight concretes with a density of up to 1700 kg/m3 of optimal compositions.Various dependencies on the evaluation of the experimental data obtained are analyzed and recommendations are given for inclusion in regulatory documents, in particular, in SP 351. 1325800.2017 "Concrete and reinforced concrete structures made of light concrete. Design rules".

Static compressive stress–strain behaviours of normal weight concrete at Arctic low temperatures

This study experimentally investigated the compressive stress–strain (σ-ε) response of normal weight concrete (NWC) at low temperatures. 72 NWC cubes and 35 NWC prisms in three grades (C25, C45, and C55) were tested under axial compression at four temperature levels (T) of −80, −60, −30, and 20 °C. The failure modes, cubic and prism compressive strength (fcuT and fcT), modulus of elasticity (EcT), and peak strain (ε0T) were studied in detail. In addition, the low-temperature effects of specimen shapes on the compressive strength of NWC were studied. These experimental results reflected that dropping T from ambient temperature to −80 °C did not influence the peak strain of NWC, but significantly increased the fcuT, fcT, and EcT of C55 NWC by 47.3 %, 69.0 %, and 45.3 %, respectively. Finally, prediction equations were established to describe the low-temperature σ-ε constitutive model of NWC. The validations confirmed that the proposed low-temperature compressive constitutive models provided reasonable predictions on the σ-ε behaviours of NWC at a T range of −80 ∼ 20 °C.

High-temperature behavior of geopolymer mortar containing nano-silica

Nano-silica (NS) can significantly improve the microstructure, mechanical properties, and durability of metakaolin/fly ash-based geopolymer mortar (GPM). To investigate the high-temperature behavior of GPM containing NS, cubic compressive strength test, prism compressive strength test, flexural strength test, visual appearance analysis, thermal strain test, thermogravimetric and differential thermal analyses, bubble parameter test, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were conducted. The NS weight contents were 0 %, 0.5 %, 1.0 %, 1.5 %, 2.0 %, and 2.5 %, and the exposure temperatures were 25, 100, 200, 400, and 600 ℃. The results revealed that the sand in mortar constrained the development of cracks when the exposure temperature was 25–200 ℃, whereas cracks formed when the temperature was 200–600 ℃. From 25 to 200 ℃, a significant mass loss with slight geopolymer shrinkage was observed. In contrast, from 200 to 600 ℃, a slight mass loss with evident shrinkage occurred. The compressive and flexural strengths of the GPM first increased when the temperature was 25–200 ℃ and then decreased when the temperature was 200–600 ℃. When the temperature was less than 200 °C, NS improved the GPM strength; however, the strength decreased when the temperature exceeded 200 ℃. The latter occurred because NS enhanced the compactness of the GPM, resulting in increased pore pressure. Additionally, the thermal stability of the phases and sodium alumina silicate hydrate structure in the geopolymer was observed. The compactness and stability of the microstructure in the GPM were enhanced by NS. A damage model based on the cubic compressive strength that well describes the relationship between the exposure temperature and degree of damage was proposed.

Analysis of milling treatments of waste clay bricks effect on density and compressive strength of cement paste

Milling treatments for evaluating grindability of pozzolanic materials using ball mill have been employed with limited studies focused on fragmented clay bricks. Of great importance of the milling treatments are sample masses. In this paper, the effects increasing sample mass of fragmented clay bricks on fineness of resulting clay brick powder (CBP) were examined using ball milling, particle size distribution curves and scanning electron microscopy (SEM). Image analysis was then used to verify variations of particle size, particle distribution, porosity and surface roughness for different sample masses. Moreover, the influence of CBP fineness on density and prismatic compressive strength of cement paste was evaluated. The reduction of sample mass fed in ball mill corresponded to enhancement of fineness of CBP. Meanwhile, image analysis proved that significant enhancement of fineness led to reduction of surface roughness. It was observed that reduced surface porosity originated from finer CBP. Findings of shape parameters showed a strong correlation for Pearson's coefficients between solidity (SLD)-circularity (Circ) pair (r ≥ 0.900, p = 0.000) and SLD-Circ relationship revealed distinguishable clusters created for the samples. Eventually, the research established that incorporating finer CBP in cement paste significantly enhanced prismatic compressive strength among CBP-cement paste mixes without significantly affecting the density of the mixes.

Mechanical properties of nano-SiO2 reinforced engineered cementitious composites after exposure to high temperatures

In this work, the effects of nano-SiO2 (NS), heating temperatures, and cooling measures on the physical, mechanical, and microscopic properties of engineered cementitious composites (ECC) after exposure to high temperatures were evaluated through a series of tests. The mass loss rate, cube, prism compressive strength, and splitting tensile strength of NS reinforced cementitious composite (NSRECC) specimens were tested after exposure to elevated temperatures of 100, 200, 300, 400, 600, and 800 °C. Changes in the color, appearance, and microstructure of the specimens were observed and discussed. The results revealed that NS has a weak effect on the color change of the specimens, whereas the heating temperature has a significant effect. The mass loss of the NSRECC specimens augmented with the temperature from 100 to 800 °C. Thus, the addition of NS to ECC can effectively enhance their mechanical characteristics after exposed to elevated temperatures by minimizing the pores and microcracks in the matrix. Notably, after exposed to a temperature of 200 ℃, the cube, and prism compressive strength and splitting tensile strength of the NSRECC specimens (with a NS content of 1 %) increased by 10.7 %, 25.1 %, and 25.6 %, respectively, as compared with those of the ECC without NS. However, the mechanical performance of the NSRECC specimens decreased markedly when the temperature exceeded 400 °C. Furthermore, the cooling measure of the specimens exhibited a certain influence over the apparent phenomenon and strength of the NSRECC after exposure to high temperatures.

Prediction of Mechanical Properties of Highly Functional Lightweight Fiber-Reinforced Concrete Based on Deep Neural Network and Ensemble Regression Trees Methods.

Currently, one of the topical areas of application of artificial intelligence methods in industrial production is neural networks, which allow for predicting the performance properties of products and structures that depend on the characteristics of the initial components and process parameters. The purpose of the study was to develop and train a neural network and an ensemble model to predict the mechanical properties of lightweight fiber-reinforced concrete using the accumulated empirical database and data from construction industry enterprises, and to improve production processes in the construction industry. The study applied deep learning and an ensemble of regression trees. The empirical base is the result of testing a series of experimental compositions of fiber-reinforced concrete. The predicted properties are cubic compressive strength, prismatic compressive strength, flexural tensile strength, and axial tensile strength. The quantitative picture of the accuracy of the applied methods for strength characteristics varies for the deep neural network method from 0.15 to 0.73 (MAE), from 0.17 to 0.89 (RMSE), and from 0.98% to 6.62% (MAPE), and for the ensemble of regression trees, from 0.11 to 0.62 (MAE), from 0.15 to 0.80 (RMSE), and from 1.30% to 3.4% (MAPE). Both methods have shown high efficiency in relation to such a hard-to-predict material as concrete, which is so heterogeneous in structure and depends on many factors. The value of the developed models lies in the possibility of obtaining additional useful information in the process of preparing highly functional lightweight fiber-reinforced concrete without additional experiments.

RELATIONSHIP BETWEEN STRENGTH AND DEFORMATION CHARACTERISTICS OF HIGH-STRENGTH SELF-COMPACTING CON-CRETE

he paper provides data on the strength and deformation characteristics of heavy self-compacting concrete of classes B30-B100 with a cubic compressive strength of 36.5-114.8 MPa. It has been established that the values of the concrete prism compressive strength (36.2-104.2 MPa) are 42-64% higher than the normalized values given in the building code of the Russian Federation SP 63.13330.2018. The values of the static modulus of elasticity for high-strength concretes of classes B80-B100 are 44.1-48.1 GPa and exceed by 5-12% the values given in SP 63.13330.2018. The ultimate compressive strains of concrete of classes B30-B100 are in the range from 261×10-5 to 326×10-5 and exceed the value of 200×10-5 given in SP 63.13330.2018. Complete deformation diagrams of self-compacting concretes of classes B30-B100 have been constructed. The nonlinearity of these ones decreases with increasing concrete strength. The descending branch of the σ-ε diagram is observed only for concrete of a class below B55 with a total relative compres-sive strain of 403.3 × 10-5 under a loading level of 0.85Rb. Concrete of classes B55-B100 has no descending branch. Previously established dependencies are refined for the analytical description of strains and stresses at any stages of loading structures.

Investigation on steel fiber strengthening of waste brick aggregate cementitious composites

The waste red brick aggregate substituted with natural coarse aggregate can effectively alleviate environmental pollution in engineering concrete constructions. However, its mechanical performance lags far behind natural coarse aggregate due to micro-pore voids and micro-cracks. Three types of steel fiber contents (0, 1%, and 2%) are selected to improve the mechanical behavior of recycled concrete in this study. Cubic compression test, splitting tensile test, prism compression test, and static compressive elastic modulus test are carried out to study the influence of steel fiber content and replacement rate of recycled coarse aggregate. In addition, the stress-strain behavior and failure mechanism of steel fiber recycled brick aggregate concrete are discussed, and microscopic crack development is also analyzed. Test results show that the specimens without steel fiber are prone to aggregate destruction under loading. The cubic and prismatic compressive strength decreased by 48% and 34%, while the splitting tensile strength reduced by 40%. The mechanical properties substantially improve when the steel fiber content is 1%. The finite element model of steel fiber recycled brick aggregate concrete under uniaxial compression is established. The constitutive model for predicting uniaxial compression of steel fiber recycled brick aggregate concrete is also proposed.

Research on optimal design of mechanical properties of hybrid fiber‐reinforced concrete

AbstractIn this study, the influence of the dosage optimization of steel fibers (SFs), basalt fibers (BFs), and polypropylene fibers (PPFs) on the mechanical properties of hybrid fiber‐reinforced concrete (HFRC) is investigated, including cube compressive strength, splitting tensile strength, and prism compressive strength. The orthogonal method was used to design the fiber mixtures to optimize the performance of the specimens. IBM SPSS Statistics software was used to analyze the significance sequence of the influencing factors of SFs, BFs, and PPFs through range and variance. The influence degree and significant affecting factors of the three fiber types were obtained, and the failure states of the HFRC specimens were analyzed. Finally, a strength prediction model for HFRC was established based on the test results. The results show that for the degree of influence on the strength of HFRC, the degree of influence of SFs was greater compared to BFs, and the degree of influence of PPFs was the smallest. In addition, for the factors that affect the strength of HFRC, the content of SFs was the primary factor, the fiber content of BFs was less important, and the content was not an important factor for PPFs. The strength prediction model established based on the orthogonal test data can well reflect the influence of three fibers types and contents on the strength of HFRC. In order to verify the validity of the present model, experimental results reported in the literature were compared with the values calculated with the present model.

Effects of spatial variability and correlation in stochastic discontinuum analysis of unreinforced masonry walls

This study investigates the influence of the uncertainty in material properties on the in-plane lateral behavior and capacity of stone masonry walls via a stochastic discontinuum analysis framework. The framework is demonstrated via the 3D numerical assessment of an unreinforced masonry (URM) wall using a stochastic analysis in the form of Monte Carlo simulations. The random parameters considered in this study are the prism compressive strength of masonry, the tensile strength of the masonry units and joints, and the friction angle for joints and units. Novel research is conducted using a fast and accurate DEM model to determine whether the spatial variability of the material properties should be taken into account. In addition, the effects of joint-to-joint correlation of modeling parameters are examined to identify if such a correlation exists. A total of 1200 stochastic discontinuum analyses for 12 different cases are carried out. The results call attention to considering the spatial variability of the modeling parameters in the stochastic analysis, as they significantly reduce the variation in the wall's strength and displacement capacity. Results also demonstrate the influence of the correlation between bed-joint parameters on the strength and failure mode of the walls. Ultimately, propagation of the uncertainty in the joint friction angle into the strength and displacement capacity of the walls is quantified.

Behavior of Confined Concrete using Prestressing Skew Bars

This paper presents the results of an experimental study on the biaxial compression behavior of concrete prism confined using pre-stressed bars. The pre-stressed bars could provide passive confinement stress, that preventing the lateral strain of the prism from increasing leading to an increase in both the initial modulus of elasticity and prism compressive strength. The confined concrete had a higher compressive strength that was directly proportional to the confinement bar pressing force and lower ductility than the plain prisms. The concrete initial modulus of elasticity is directly proportioned to the confinement lateral pressure of the prestressing bar and inversely proportion with the spacing between prestressing bars. It was simple to find out that the best pre-stressing stress was 10 N/mm2, also the compressive strength of the confined concrete with pre-stressed skew bars was greater than the compressive strength of the unconfined concrete by more 3.3 times.

Grindability Evaluation of Fragmented Clay Bricks for Performance Analysis of Cement Paste Incorporating Clay Brick Powder

.Milling treatments for evaluating grindability of pozzolanic materials using ball mill have been employed with limited research focused on fragmented clay bricks. Of great importance of the milling treatments are the milling times and sample masses. Moreover, the applications of grindability of Clay Brick Powder (CBP) in cement paste are found to be limited. In this paper, the effects of increasing milling time and increasing sample mass of fragmented clay bricks on fineness of resulting CBP were examined using ball milling and particle size distribution curves. The Scanning Electron Microscope (SEM) was implemented to characterise the morphological properties of CBP. Compliance of CBP with minimum requirements for pozzolanic characteristics was verified using X-Ray Fluorescence and X-Ray Diffraction. Extensive Image analysis using ImageJ and Origin was employed to verify significant variations of particle size, particle distribution, porosity and surface roughness for different sample mass. Properties of cement paste containing CBP were assessed to capture essential elements on the influence of CBP fineness on density and prismatic compressive strength of cement paste. The overall influence of grinding illustrated that a decline in particle size of CBP was facilitated in samples subjected to prolonged milling times. On the other hand, the reduction of sample mass fed in ball mill corresponded to enhancement of fineness of CBP. Meanwhile, qualitative evaluation of three-dimensional reconstruction of SEM images using ImageJ proved that significant enhancement of fineness led to reduction of surface roughness. Quantification of surface porosity demonstrated that reduced surface porosity originated from finer CBP. Consequently, the research established the feasibility of incorporating finer CBP in cement paste, which significantly contributes to enhancement of prismatic compressive strength. Concerning cement paste density, the inclusion of CBP in cement was not of significant consequence on its density due to similar packing densities of CBP.

EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES AND CONSTITUTIVE RELATIONSHIP OF STEEL SLAG AGGREGATE REINFORCED CONCRETE

In order to study the applicability of steel slag coarse aggregate in concrete and the uniaxial compression performance of steel slag concrete, the physical and chemical properties of steel slag aggregate were tested, and the stability of steel slag coarse aggregate was tested and analyzed. Six groups of steel slag concrete cube and prism specimens with different steel slag coarse aggregate content were prepared, and the uniaxial compression performance of steel slag concrete was studied. The results show that the free calcium oxide, water immersion expansion rate and autoclaved pulverization rate of steel slag used in this paper meet the requirements of relevant specifications and are suitable for concrete aggregate;the brittle characteristics of steel slag coarse aggregate concrete are more obvious than ordinary concrete; the ratio of prism compressive strength of steel slag concrete to cube compressive strength is 0.83-0.9. The constitutive relationship of steel slag concrete can be described stage by stage according to the constitutive model by GUO Zhenhai and Wee model. The stage-based constitutive model is basically consistent with the measured stress-strain curve of steel slag coarse aggregate concrete.

Research of physicomechanical and design characteristics of vibrated, centrifuged and vibro-centrifuged concretes

Introduction. Currently, the obtaining of lightweight concrete and reinforced concrete products and structures with the improved structure and characteristics is a challenge. This can be achieved through centrifugation or in a more advanced way — vibro-centrifugation. At the same time, the influence of centrifugal and centripetal forces of inertia in these types of technologies causes differences in the cross-section properties of concrete products and structures. To reflect this in the calculations, it is required to experimentally and analytically investigate the qualitative and quantitative patterns of such differences in the characteristics of concretes obtained through different technologies. Materials and Methods. The study used the cross-section averaged characteristics of concrete — “integral characteristics of concrete”. The applicable raw materials included portland cement 500, crushed stone fraction 5-20, medium sand. Nine control samples of annular cross-section obtained through vibrating, centrifuging, and vibro- centrifugation were manufactured and tested. The essence of the technique was that each manufactured experimental control sample was used in several types of tests in-parallel. From the total annular section of each sample, three conditional quadrants were distinguished, from which standard samples of small size were cut out. Subsequently, they were tested for axial compression, tension, and flexural tension. The following test equipment was used: electronically controlled mechanical press IPS-10 — for compression testing of prisms, and the breaking machine R-10 — for testing samples for axial tension. Strain sensors and dial indicators were used to measure concrete deformations. Oscilloscopes were also used to obtain the deformative and strength properties of concrete, including full deformation diagrams with descending branches. Results. We have analyzed the calculation results of the integral design characteristics of the concretes obtained through vibration, centrifugation and vibro-centrifugation. It is established that due to the influence of centrifugal and centripetal forces of inertia under centrifugation and vibration centrifugation, the characteristics of concrete in cross-section become different. In some cases, these differences can be very significant. We have developed and tested the following: a new method for evaluating the dependence of the integral (cross–section averaged) design characteristics of concrete (density, cubic and prismatic axial compressive strength); ultimate deformations under axial compression; axial tensile and flexural tensile strength; ultimate deformations under axial tension; elasticity modulus; diagram of “stress ϭb– strain εb” under compression; diagram of “stress ϭbt–strain εbt” under tension on the manufacturing technology (vibrating, centrifuging, vibration centrifugation). Discussion and Conclusions. Based on the results of the research, conclusions are formulated on the positive effect of the proposed technology of joint vibrating and centrifuging. It consists in improving the integral design characteristics and structure of concrete from vibrating to centrifuging and from centrifuging to vibro-centrifuging.

Grading Method of Mixed Recycled Coarse Aggregate

Due to the limitations of sorting technology, mixed recycled coarse aggregate, which mainly includes recycled concrete coarse aggregate and recycled brick coarse aggregate, accounts for a large proportion of recycled aggregate. This paper proposes a grading method for mixed recycled coarse aggregate to ensure satisfactory concrete performance. Distribution of specific density, saturated surface dry density, water absorption, and crushing value of mixed recycled coarse aggregate, as well as the effect of recycled brick coarse aggregate content, on the four parameters of mixed recycled coarse aggregate are investigated in this paper. The water absorption and crushing value were selected as the main grading indexes of mixed recycled coarse aggregate by using the weighted grey analysis method. According to the analysis results of the nonlinear fitting curves between the property indexes of mixed recycled coarse aggregate (water absorption and crushing value) and the performance parameters of mixed recycled coarse aggregate concretes (cubic compressive strength, prism compressive strength, splitting tensile strength, static modulus of elasticity, and the flexural strength), the mixed recycled coarse aggregates were divided into two categories; Categories I and II are used for structure and nonstructure uses, respectively.