• Advances in concrete construction
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• 제6권2호
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• pp.145-157
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• 2018

This paper presents a review on the use of Silica Fume (SF) as a mineral admixture in the concrete. Distinctive outcome from several researches have been demonstrated here, particularly emphasizing on the fresh and hardened properties of concrete when blended with Silica Fume (Micro-silica or Nano-silica). The results showed a substantial enhancement in the mechanical properties of concrete when replaced with SF. The review also presented a brief idea of percentage replacement of SF in case of normal and high-strength concrete. A decreasing trend in workability (slump value) has been identified when there is a increase in percentage replacement of SF. It can be concluded that the optimize percentage of replacement with SF lies in the range of 8-10% particularly for compressive strength. However the variation of blending goes up to 12-15% in case of split tensile and flexure strength of concrete. The study also demonstrates the effect of silica fume on durability parameters like water absorption, permeability, sulphate attack and chloride attack.

• Geomechanics and Engineering
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• 제29권4호
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• pp.451-461
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• 2022

The roadways surrounded by rock and coal will lose their stability or even collapse under rock burst. Rock burst mainly involves an evolution of dynamic loading which behaves quite differently from static or quasi-static loading. To compare the dynamic response of coal and rocks with different static strengths, three different rocks and bituminous coal were selected for testing at three different dynamic loadings. It's found that the dynamic compression strength of rocks and bituminous coal is much greater than the static compression strength. The dynamic compression strength and dynamic increase factor of the rocks both increase linearly with the increase of the strain rate, while those of the bituminous coal are irregular due to the characteristics of multi-fracture and heterogeneity. Moreover, the absorbed energy of the rocks and bituminous coal both increase linearly with an increase in the strain rate. And the ratio of absorbed energy to the total energy of bituminous coal is greater than that of rocks. With the increase of dynamic loading, the failure degree of the sample increases, with the increase of the static compressive strength, the damage degree also increases. The static compassion strength of the bituminous coal is lower than that of rocks, so the number of small-scale fragments was the largest after bituminous coal rupture.

• Steel and Composite Structures
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• 제31권6호
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• pp.559-573
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• 2019

Spiral spacing effect on axial compressive behavior of reinforced concrete filled steel tube (RCFST) stub column is experimentally investigated in this paper. A total of twenty specimens including sixteen square RCFST columns and four benchmarked conventional square concrete filled steel tube (CFST) columns are fabricated and tested. Test variables include spiral spacing (spiral ratio) and concrete strength. The failure modes, load versus displacement curves, compressive rigidity, axial compressive strength, and ductility of the specimens are obtained and analyzed. Especially, the effect of spiral spacing on axial compressive strength and ductility is investigated and discussed in detail. Test results show that heavily arranged spirals considerably increase the ultimate compressive strength but lightly arranged spirals have no obvious effect on the ultimate strength. In practical design, the effect of spirals on RCFST column strength should be considered only when spirals are heavily arranged. Spiral spacing has a considerable effect on increasing the post-peak ductility of RCFST columns. Decreasing of the spiral spacing considerably increases the post-peak ductility of the RCFSTs. When the concrete strength increases, ultimate strength increases but the ductility decreases, due to the brittleness of the higher strength concrete. Arranging spirals, even with a rather small amount of spirals, is an economical and easy solution for improving the ductility of RCFST columns with high-strength concrete. Ultimate compressive strengths of the columns are calculated according to the codes EC4 (2004), GB 50936 (2014), AIJ (2008), and ACI 318 (2014). The ultimate strength of RCFST stub columns can be most precisely evaluated using standard GB 50936 (2014) considering the effect of spiral confinement on core concrete.

• Advances in concrete construction
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• 제8권1호
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• pp.1-7
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• 2019

The possibility of using recycled coarse glass aggregates as a substitute for natural crushed stone are relatively limited. In order to promote it for engineering application, this paper reports the effect of coarse glass aggregate on mechanical behavior of concrete. The coarse aggregates are substituted for coarse glass aggregate (CGA) as 0%,20%,40%,60%,80% and 100%.The results show that increasing the coarse glass aggregate content cause decrease in compressive strength, the elastic modulus, the splitting tensile strength, the flexural strength. An equation is presented to generate the relationship between cube compressive strength and prism compressive strength, the relationship between cube compressive strength and elastic modulus, the relationship between cube compressive strength and splitting tensile strength, the relationship between cube compressive strength and flexural strength of coarse glass concrete.

• Structural Engineering and Mechanics
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• 제80권6호
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• pp.689-699
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• 2021

The present study aims to understand the behaviour of low-strength masonry prisms constructed with locally-produced low-strength hollow concrete blocks. Compression tests were conducted on masonry prisms constructed with three different mortar grades of cement-sand ratios of 1:3, 1:4.5 and 1:6 representing strong, moderately strong and weak mortar. Stress-strain curves were generated from the test results for the masonry prisms. The hollow concrete masonry units employed in this study are some of the weakest as compared to other masonry units employed by other researchers. The compressive strengths for masonry prisms with mortar grades 1:3, 1:4.5 and 1:6 are 2.21 MPa, 2.19 MPa and 2.25 MPa respectively. The results indicate that the masonry compressive strength of such low-strength hollow concrete block masonry prisms is not influenced by the mortar strength. Simple relationships to estimate the modulus of elasticity and compressive strength of masonry prisms is also proposed.

• Advanced Composite Materials
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• 제18권4호
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• pp.315-326
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• 2009

PCC (precipitated calcium carbonate) and ground calcium carbonate have been widely used in alkaline papermaking. Unfortunately, although increasing filler level in papers can improve the paper properties such as brightness, opacity, stiffness gloss, smoothness, porosity, and printability, as well as decrease cost, some strength of the paper is negatively affected. In this research, needle-like aragonite was synthesized using $Ca(OH)_2$ and $CO_2$ as reactants in the presence of $MgCl_2$ and characterized with scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The physical and optical properties of the paper handsheets containing these needle-like aragonite fillers were evaluated. Results indicated that tensile strength, Z-direction tensile strength and folding endurance of the paper were improved by the needle-like aragonite crystals compared to the paper using commercial PCC (precipitated calcium carbonate) as filler. The stiffness of the paper handsheet on the machine direction was increased, but no evident difference in the cross direction was found. The improvement of paper strength mainly resulted from the twining effect between the aragonite whiskers and paper fibers. The optical properties of the paper were slightly decreased with the use of the needle-like aragonites compared to commercial PCC. These results suggest that paper cost can be decreased by increasing the content of needle-like aragonite filler while paper strength will not be decreased compared to PCC filler.

• Steel and Composite Structures
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• 제18권6호
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• pp.1517-1539
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• 2015

Eccentrically braced frames (EBFs) often use conventional steel with medium yield strength. This system requires structural members with large cross-sections for well seismic behavior, which leads to increased material costs. In eccentrically braced frames with high strength steel combination (HSS-EBFs), links use Q345 steel (specified nominal yield strength 345 MPa), braces use Q345 steel or high strength steel while other structural members use high strength steel (e.g., steel Q460 with the nominal yield strength of 460 MPa or steel Q690 with the nominal yield strength of 690 MPa). For this approach can result in reduced steel consumption and increased economic efficiency. Several finite element models of both HSS-EBFs and EBFs are established in this paper. Nonlinear hysteretic analyses and nonlinear time history analyses are conducted to compare seismic performance and economy of HSS-EBFs versus EBFs. Results indicate that the seismic performance of HSS-EBFs is slightly poorer than that of EBFs under the same design conditions, and HSS-EBFs satisfy seismic design codes and reduce material costs.

• Computers and Concrete
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• 제14권3호
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• pp.327-345
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• 2014

This paper presents the application of multi-gene genetic programming (MGP) technique for modeling the bond strength of ribbed steel bars in concrete. In this regard, the experimental data of 264 splice beam tests from different technical papers were used for training, validating and testing the model. Seven basic parameters affecting on the bond strength of steel bars were selected as input parameters. These parameters are diameter, relative rib area and yield strength of steel bar, minimum concrete cover to bar diameter ratio, splice length to bar diameter ratio, concrete compressive strength and transverse reinforcement index. The results show that the proposed MGP model can be alternative approach for predicting the bond strength of ribbed steel bars in concrete. Moreover, the performance of the developed model was compared with the building codes' empirical equations for a complete comparison. The study concludes that the proposed MGP model predicts the bond strength of ribbed steel bars better than the existing building codes' equations. Using the proposed MGP model and building codes' equations, a parametric study was also conducted to investigate the trend of the input variables on the bond strength of ribbed steel bars in concrete.

• 한국안전학회지
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• 제25권2호
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• pp.41-46
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• 2010

This is to show some basic data for introducing both circulated aggregate and recycled powder producing waste concrete. Standard-mixing design for 24MPa has been basically used and added and replaced normal aggregate with recycled powder made of waste concrete. In addition, polycarboxylate high-range water reducing agent has been used because recycled powder is missing adhesive strength and it is not compare with cement's adhesive strength. Compressive strength with powder mixture of 2%, 4%, 6%, 8%, and 10% has been decreased down to 80% of normal concrete material strength without recycled powder mixture. This result has same decreasing proportion to tensile strength of the material. Resistant capacity change of beam varying with recycled powder mixture has been decreased down to 60% of normal concrete bean capacity, while there are 80% decrease of material strength. But strength and capacity change has same consistent decrease ratio. It is found that recycled powder with approximately 15% unit concrete volume can be replaced with cement in reasonable admixture mixing condition.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.876-883
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• 2023

Radioactive waste should be solidified before being disposed of in the repository to eliminate liquidity or dispersibility. Cement is a widely used solidifying media for radioactive waste, and cement solidified waste should satisfy the minimum compressive strength of the waste acceptance criteria of a radioactive repository. Although the compressive strength of waste should be measured by the test method provided by the waste acceptance criteria, the method differs depending on the operating repository of different countries. Considering the measured compressive strength changes depending on test conditions, the effect of test conditions should be analyzed to avoid overestimation or underestimation of the compressive strength during disposal. We selected test conditions such as the height-to-diameter ratio, loading rate, and porosity as the main factors affecting the compressive strength of cement solidified radioactive waste. Owing to the large variance in measured compressive strength, the effects of the test conditions were analyzed via statistical analyses using parametric and nonparametric methods. The results showed that the test condition of the lower loading rate, with a height-to-diameter ratio of two, reflected the actual cement content well, while the porosity showed no correlation. The compressive strength assessment method that reflects the large variance of strengths was suggested.