Magazine of Concrete Research
ISSN / EISSN : 0024-9831 / 1751-763X
Published by: Thomas Telford Ltd. (10.1680)
Total articles ≅ 4,157
Latest articles in this journal
Magazine of Concrete Research pp 1-36; https://doi.org/10.1680/jmacr.21.00221
This study reports the test results for eight high-strength concrete square pile caps. The main variables are area of flexural steel bars and the configuration patterns of flexural steel bars. The test results show that the ultimate load on the pile cap increases as the total area of the flexural steel bars increases. The load-displacement curves are not significantly affected by an increase in the total area of the flexural steel bars. For a specific area of flexural steel bar, the ultimate load on pile caps in a bunched square reinforcement pattern is no greater than that for pile caps in a grid reinforcement pattern. Pile caps in a bunched square reinforcement pattern exhibit no significant mechanical advantage over pile caps in a grid reinforcement pattern. Square pile caps in a grid reinforcement pattern perform better because this pattern is more conducive to concrete casting than a bunched square reinforcement pattern. The softened strut-and-tie (SST) model more accurately predicts the ultimate load for pile caps than the ACI Sectional method for various shear span-to-depth ratios and compressive strengths of concrete. The ACI Sectional method overestimates the flexural strength of the square pile cap.
Magazine of Concrete Research pp 1-36; https://doi.org/10.1680/jmacr.21.00110
This study focused on the effects of changing the types and surface areas (Sa) of activated materials on the compressive strength of Ground Granulated Blast-furnace Slag (GGBS) cement (GGBS > 60%). This study is divided into two parts. The first part involves the selection of activated materials. The compressive strength results show that gypsum improves the early strength of GGBS cement more effectively that does sodium silicate or NaOH. The gypsum activators increase GGBS activity through sulfates, which generates ettringites and C-S-H to increase compressive strength. Chemical analysis shows that the SO3 in GGBS cement has more stable compressive strength at 6%–8%. The second part of this study is on the influence of Sa. Gypsum was used as a strength activator. The SO3 in GGBS cement was controlled at 6.5%±0.5%, and Sa was adjusted as the variable. Linear regression analysis shows that the change in GGBS cement Sa (MSa) is positively correlated with compressive strength. The MSa can be estimated according to the Sa and quantity of ingredients used for the study results (cement, GGBS, and gypsum). The compressive strengths of GGBS cement at various curing ages can be predicted with MSa.
Magazine of Concrete Research pp 1-30; https://doi.org/10.1680/jmacr.21.00159
Plastic shrinkage cracking propagating at early ages inevitably impairs the performance of concrete structures. To mitigate it, using a recently developed shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) with outstanding shrinkage-reducing and water-reducing effectiveness can be a promising approach. This present work aims at investigating the effect of the SR-PCA on the plastic shrinkage cracking and clarifying the underlying mechanisms. For comparison, a traditional polyether type shrinkage reducing admixture (SRA) and a polycarboxylate superplasticizer (PCA) were also used. Based on the investigations on horizontal shrinkage, settlement, bleeding, evaporation mass loss, cement hydration, surface tension of pore fluid and capillary pressure, the underlying working mechanisms of SR-PCA were identified. The results indicate that the SR-PCA is able to reduce the crack area, maximum crack width and average crack width by up to 55%, 48% and 50%, respectively. Furthermore, prolonging the bleeding duration and initial time of capillary pressure build-up caused by retarding the cement hydration, lowering the evaporation mass loss, and a lower development rate of capillary stresses and capillary pressure peak value induced by decreasing the surface tension of pore fluid are responsible for preventing the plastic shrinkage cracking of mortars containing SR-PCA.
Magazine of Concrete Research, Volume 73, pp 988-1010; https://doi.org/10.1680/jmacr.19.00542
Different macro models have been proposed in the past decades for simulating the behavior of concrete shear walls because of their significant role in the seismic performance of urban buildings. In this paper, the ability of Timoshenko's beam theory to evaluate the behavior of slender and moderate-aspect-ratio concrete shear walls is evaluated. For this purpose, a nonlinear displacement-based Timoshenko fiber element was first added to OpenSees software. A new constitutive model based on modified compression field theory was used for the stress-strain relationship of the materials. To validate the utilized element and materials, the results of the numerical model were compared with a set of laboratory tests of concrete shear walls subjected to cyclic and seismic loads (shaking-table test). Evaluating the numerical model and the experimental results revealed that the analysis procedure is presented to model the RC walls predicts the overall and local response of the wall with acceptable accuracy and thus can be used as a reliable tool for the analysis of slender and moderate-aspect-ratio concrete shear walls.
Magazine of Concrete Research, Volume 73, pp 1048-1059; https://doi.org/10.1680/jmacr.19.00371
Refractory concretes are widely applied for the lining of steel shell of industrial structures subjected to high temperatures and pressure. Working linings of steel ladles are made of high alumina concretes applied in layers that receive heat flow. Modeling the thermo-mechanical behavior of these layers under service conditions is of paramount importance to evaluate the failure or cracking that determine their useful life. In this work, simulations of the heating and holding process of linings composed of several layers of different types of refractory with different alumina contents (51, 71 and 90wt%), previously studied, were performed. The developed model employed axisymmetric finite elements and the thermo-mechanical analyses were carried out using the ABAQUS software package. The results of the thermo-mechanical response were compared and it was observed that the combination using the refractory concrete with 90 wt.% of alumina as an inner layer, combined with materials of 71wt.% and 51wt.% as the middle and outer layers, respectively, is more efficient in terms of the thermal gradient. Therefore, would potentially lead to minor damage to the lining throughout the process of use. This indicates the importance of selection of the coating materials for application in layers.
Magazine of Concrete Research, Volume 73, pp 1071-1080; https://doi.org/10.1680/jmacr.19.00436
Self-compacting concrete (SCC) are widely used in tunnel linings that are subjected to the risks of fire accident. During tunnel fire, personnel and structural safety are commonly threatened by explosive spalling of SCC due to high strength and high moisture content of SCC. Recent studies have suggested that coating layer of fire-resistant material can efficiently prevent SCC from spalling in tunnel fire. In this study, SCC samples coated with 6 mm SiO2 aerogel-cement mortar (SiO2-ACM) were prepared in comparison with those without coating. The effects of different moisture contents (0%, 25%, 50%, 75%, and 100%) on the fire resistance of SCC were investigated. The results show that SiO2-ACM exhibited excellent mechanical and durable performances and low thermal conductivity. During the exposure to the mimetic tunnel fire, the degree of spalling of SCC increased as moisture content increased. The SCC samples with SiO2-ACM coating exhibited much less spalling than those without coating. After mimetic tunnel fire, bare SCC had almost completely failed in compressive strength, whereas residual compressive strength of SCC coated with SiO2-ACM were more than 68.6% even SCC with 100% of moisture content. Therefore, SiO2-ACM coating provides an attractive avenue to enhance the behavior of SCC in tunnel fire.
Magazine of Concrete Research, Volume 73, pp 1025-1032; https://doi.org/10.1680/jmacr.19.00559
The Compressible Packing Model (CPM) is used to calculate the packing density of quartz aggregate, which is a new method for designing aggregate gradation. In this paper, the aggregate gradation of ultra high performance concrete (UHPC) was optimized by the CPM. The number of interfaces between the aggregate and cement was counted by Image Pro Plus software. The results show that the CPM was modified by the equation Y=0.60073X+0.20551 to accurately calculate the packing density of quartz aggregate. The compressive strength of UHPC was positively correlated with the packing density of the aggregate. By increasing the packing density, the compressive strength of UHPC was increased from 97.9 MPa to 124.1 MPa, an increasing of 26.7%. The flexural strengths of the materials was sensitive to the number of interfaces. The smaller the number of interfaces was, the greater the flexural strength. The specimen with an interface of 5.56mm/mm2 had the smallest flexural strength of 21.5 MPa, the specimen with an interface of 3.596 mm/mm2 had the largest flexural strength of 25.9 MPa. When designing aggregate gradation, a gradation with high density should be selected, and the proportion of small-size aggregates should not be too large.
Magazine of Concrete Research, Volume 73, pp 973-987; https://doi.org/10.1680/jmacr.19.00485
This paper investigates the physical, chemical, and mechanical properties of concrete produced with rejected recyclable plastic waste, the potential to mitigate heat-induced concrete spalling, and the effects of high temperature on the residual properties of concrete. Concrete compressive and tensile strength, Young's modulus, crack width, mass loss, absorption by capillarity, chemical composition, and the evidence of heat-induced concrete spalling have been monitored in concrete samples produced with plastic waste particles and compared to that of concrete produced with commercial polypropylene fibers, after exposure to 200oC, 400oC, and 600oC for 2 hours. The use of 0.125% by volume of polypropylene fibers and plastic waste particles have proved to improve the heat-induced concrete spalling performance, contributing to the release of internal pressure after melting by different mechanisms. Positive effects in the concrete properties evidence the technical potential of incorporating rejected recyclable plastic waste particles in the construction chain.
Magazine of Concrete Research, Volume 73, pp 1011-1024; https://doi.org/10.1680/jmacr.19.00558
Microstructure and transport properties of graphene oxide (GO)-cement mortars with similar consistency were experimentally investigated and compared with those of control mortars that were made using Portland cement. Polycarboxylate superplasticizer (PCs) was used to improve the consistency of GO-modified mortars and the dispersibility of GO nanosheets. Results indicate that the GO-incorporating mortars with similar consistency reduce the chloride migration coefficient and the initial rate of water absorption by 33.2% and 61.6% compared with the control samples, respectively. This improvement is due to the addition of GO particles in the mortars which inhibit crack growth, change the morphology of hydrated crystals and refine the pore structure. Meanwhile, very small amounts of GO additives can significantly decrease the macropore volume fraction and the critical as well as average pore diameters. To understand the correlation between the pore-size distribution and the macroscopic transport performance, both the critical pore diameter and the macropore volume fraction have been proved to be exponentially dependent on chloride migration coefficient. The average pore diameter is linearly related to the initial absorption rate of the mortars, but is independent of the secondary absorption rate.
Magazine of Concrete Research, Volume 73, pp 1033-1047; https://doi.org/10.1680/jmacr.19.00459
The bond between reinforcement and concrete is one of the main factors affecting the structural performance. In terms of the bond mechanism, the bond performance of plain round bars is especially sensitive to the stress state of surrounding concrete. Lateral tensions have been confirmed to significantly weaken the bond properties of plain round bars but the effect of loading rate on such a condition is still not well understood. In the present paper, an experiment involving 178 pull-out specimens with various strengths of concrete and bar diameters is performed to analyse the influence of loading rate on the bond behaviour of plain round bars embedded in concrete under uniaxial lateral tensions. The main bond parameters are evaluated quantitatively. The results show that the bond strength is independent of loading rate and the ratio between the residual strength and the bond strength keeps constant, but the slip at the peak bond stress decreases obviously with increasing the loading rate. Finally, an empirical constitutive model of bond stress-slip considering the strength of concrete, the bar diameter, uniaxial lateral tensions, and the loading rate is presented and validated with experimental results.