Showing papers on "Compressive strength published in 2011"
TL;DR: In this paper, ground fly ash (GFA), with a median particle size of 10.5μm, was used as source material for making geopolymers cured at room temperature, and compressive strength tests and microstructure observations using SEM, EDX, XRD and FTIR were performed.
755 citations
TL;DR: In this article, the microstructure of three AASs with MgO contents between 8 and 13.5% were investigated and the formation of C(−−A)−S−H and a hydrotalcite-like phase was observed in all samples by X-ray diffraction (XRD), thermal analysis (TGA) and scanning electron microscopy (SEM) techniques.
685 citations
TL;DR: In this article, the hydration of two slags with different Al 2 O 3 contents activated with sodium hydroxide and hydrous sodium metasilicate (commonly named water glass) was studied using a multi-method approach.
685 citations
TL;DR: In this paper, the performance of natural and recycled aggregate concrete prepared with the incorporation of different mineral admixtures including silica fumes (SF), metakaolin (MK), fly ash (FA) and Ground granulated blast slag (GGBS) was determined.
Abstract: This paper presents the results of a laboratory study on the performance of natural and recycled aggregate concrete prepared with the incorporation of different mineral admixtures including silica fumes (SF), metakaolin (MK), fly ash (FA) and Ground granulated blast slag (GGBS). The compressive and splitting tensile strength, drying shrinkage, chloride ion penetration and ultrasonic pulse velocity (UPV) of the concrete mixtures were determined. The test results, in general, showed that the incorporation of mineral admixtures improved the properties of the recycled aggregate concretes. SF and MK contributed to both the short and long-term properties of the concrete, whereas FA and GGBS showed their beneficial effect only after a relatively long curing time. As far as the compressive strength is concerned, the replacement of cement by 10% of SF or 15% of MK improved both mechanical and durability performance, while the replacement of cement by 35% FA or 55% GGBS decreased the compressive strength, but improved the durability properties of the recycled aggregate concretes. Moreover, the results show that the contributions of the mineral admixtures to performance improvement of the recycled aggregate concrete are higher than that to the natural aggregate concrete.
467 citations
TL;DR: In this article, the authors describe the development of a UHPC with a compressive strength exceeding 200 MPa (30 ksi), obtained using materials commercially available in the U.S. market and without the use of any heat treatment, pressure or special mixer.
Abstract: Although intensive research related to ultra high-performance concrete (UHPC) and its composition has been conducted over the past 2 decades, attaining compressive strengths of over 150 MPa (22 ksi) without special treatment, such as heat curing, pressure, and/or extensive vibration, has been nearly out of reach. This paper describes the development of a UHPC with a compressive strength exceeding 200 MPa (30 ksi), obtained using materials commercially available in the U.S. market and without the use of any heat treatment, pressure, or special mixer. The influence of different variables such as type of cement, silica fume, sand, and high-range water reducer on compressive strength is evaluated. The test results show that the spread value, measured through a slump cone test on a flow table, is a good and quick indicator to optimize the mixture packing density and thus its compressive strength.
426 citations
15 Nov 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a three-step mixing method was used to improve the wettability and distribution of reinforcement particles within the matrix, which included heat treatment of micro and nano Al2O3 particles, injection of heat-treated particles, and stirring the melt at different speeds.
Abstract: Aluminum matrix composites (AMCs) reinforced with micro and nano-sized Al2O3 particles are widely used for high performance applications such as automotive, military, aerospace and electricity industries because of their improved physical and mechanical properties. In this study, in order to improve the wettability and distribution of reinforcement particles within the matrix, a novel three step mixing method was used. The process included heat treatment of micro and nano Al2O3 particles, injection of heat-treated particles within the molten A356 aluminum alloy by inert argon gas and stirring the melt at different speeds. The influence of various processing parameters such as heat treatment of particles, injection process, stirring speed, reinforcement particle size and weight percentage of reinforcement particles on the microstructure and mechanical properties of composites was investigated. The matrix grain size, morphology and distribution of Al2O3 nanoparticles were recognized by scanning electron microscopy (SEM), optical microscope (OM) equipped with image analyzer, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Also, the hardness and compression strength of samples was investigated. The results showed the poor incorporation of nano particles in the aluminum melt prepared by the common condition. However, the use of heat-treated particles, injection of particles and the stirring system improved the wettability and distribution of the nano particles within the aluminum melt. In addition, it was revealed that the amount of hardness, compressive strength and porosity increased as weight percentage of nano Al2O3 particles increased.
404 citations
TL;DR: In this article, the authors developed a mathematical model to characterize the relationship between compressive strength and porosity for porous concrete by analyzing empirical results and theoretical derivations, which was derived from Griffith's theory.
402 citations
TL;DR: The test results indicate that the Thermal conductivity is substantially improved with the use of perlite and a strong relationship between thermal conductivity and unit weight is obtained.
389 citations
TL;DR: In this paper, the authors evaluated the mechanical and durability performance of concretes produced using alkali silicate-activated ground granulated blast furnace slag as sole binder.
381 citations
TL;DR: In this paper, the physical, chemical properties of silica fume and its reaction mechanism are investigated for workability, porosity, compressive strength, splitting tensile strength, flexural strength, creep and shrinkage of concrete.
Abstract: Several types of industrial byproducts are generated. With increased environmental awareness and its potential hazardous effects, utilization of industrial byproducts has become an attractive alternative to disposal. One such by-product is silica fume (SF), which is a byproduct of the smelting process in the silicon and ferrosilicon industry. Silica fume is very effective in the design and development of high strength high performance concrete. This paper covers the physical, chemical properties of silica fume, and its reaction mechanism. It deals with the effect of silica fume on the workability, porosity, compressive strength, splitting tensile strength, flexural strength, creep and shrinkage of concrete.
378 citations
TL;DR: In this paper, the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC) was investigated.
Abstract: This paper investigates the influence of different amounts of recycled coarse aggregates obtained from a demolished RCC culvert 15 years old on the properties of recycled aggregate concrete (RAC). A new term called “coarse aggregate replacement ratio (CRR)” is introduced and is defined as the ratio of weight of recycled coarse aggregate to the total weight of coarse aggregate in a concrete mix. To analyze the behaviour of concrete in both the fresh and hardened state, a coarse aggregate replacement ratio of 0, 0.25, 0.50 and 1.0 are adopted in the concrete mixes. The properties namely compressive and indirect tensile strengths, modulus of elasticity, water absorption, volume of voids, density of hardened concrete and depth of chloride penetration are studied. From the experimental results it is observed that the concrete cured in air after 7 days of wet curing shows better strength than concrete cured completely under water for 28 days for all coarse aggregate replacement ratios. The volume of voids and water absorption of recycled aggregate concrete are 2.61 and 1.82% higher than those of normal concrete due to the high absorption capacity of old mortar adhered to recycled aggregates. The relationships among compressive strength, tensile strengths and modulus of elasticity are developed and verified with the models reported in the literature for both normal and recycled aggregate concrete. In addition, the non-destructive testing parameters such as rebound number and UPV (Ultrasonic pulse velocity) are reported. The study demonstrates the potential use of field recycled coarse aggregates (RCA) in concrete.
TL;DR: In this paper, the authors examined the durability properties of the recycled aggregate concrete (RAC) and showed that the RAC exhibits a good UPV value, low water absorption and low intrinsic permeability.
TL;DR: In this article, an ultra high performance fiber reinforced concretes (UHP-FRC) with a compressive strength of 200 MPa (29 ksi) providing high bond strength between fiber and matrix was developed.
Abstract: This research work focuses on the optimization of strength and ductility of ultra high performance fiber reinforced concretes (UHP-FRC) under direct tensile loading. An ultra high performance concrete (UHPC) with a compressive strength of 200 MPa (29 ksi) providing high bond strength between fiber and matrix was developed. In addition to the high strength smooth steel fibers, currently used for typical UHP-FRC, high strength deformed steel fibers were used in this study to enhance the mechanical bond and ductility. The study first shows that, with appropriate high strength steel fibers, a fiber volume fraction of 1% is sufficient to trigger strain hardening behavior accompanied by multiple cracking, a characteristic essential to achieve high ductility. By improving both the matrix and fiber parameters, an UHP-FRC with only 1.5% deformed steel fibers by volume resulted in an average tensile strength of 13 MPa (1.9 ksi) and a maximum post-cracking strain of 0.6%.
TL;DR: In this paper, the influence of supplementary cementitious materials (SCMs), namely silica fume, metakaolin, fly ash and ground granulated blast-furnace slag, on the engineering properties of high strength concrete (HSC) has been investigated in order to quantify the effects of different materials.
TL;DR: In this article, the physicico-mechanical behavior of nano metakaolin and nano-clay was studied and the results showed that, the replacement of OPC by 6 ¾wt.% NMK increases the compressive strength of blended mortar by 18% compared to control mix and the combination of 6 ¼ wt.%.
TL;DR: In this article, a comprehensive study on the durability properties of concrete containing polypropylene fiber and fly ash was performed, and the results showed that the positive interactions between polypropane fibers and fly-ash lead to the lowest drying shrinkage of fibrous concrete with fly ash.
TL;DR: In this article, the authors investigated the potential use of recycled tire rubbers in cement matrices, which facilitates the development of concrete with a lesser environmental impact and contributes to developing construction in a sustainable way.
TL;DR: In this article, the effects of adding residual rice husk ash (RHA) from South Vietnam, generated when burning Rice husk pellets in the boiler, to cement were investigated.
TL;DR: In this paper, the influence of replacing natural coarse aggregate with recycled concrete aggregate (RCA) has been investigated on concrete bond strength with reinforcing steel, and two sources of RCA were used along with one natural aggregate source.
TL;DR: In this article, the effect of mix design parameters on the compressive strength and thermal performance of alkali silicate-activated blends of metakaolin (MK) and granulated blast furnace slag (GBFS) was assessed.
Abstract: This article assesses the effect of mix design parameters on the compressive strength and thermal performance of alkali silicate-activated blends of metakaolin (MK) and granulated blast furnace slag (GBFS). A strong interrelationship between the effects of activator composition and the GBFS/(GBFS + MK) ratio is identified through statistical analysis of compressive strength data. Pastes formulated with higher SiO2/Al2O3 molar ratios show improvements in mechanical strength with increasing GBFS addition, associated with the formation of a structure comprising coexisting aluminosilicate ‘geopolymer’ gel and Ca-rich Al-substituted silicate hydrate (C-(A)-S-H) reaction products. The inclusion of GBFS in MK-based geopolymers seems also to improve their performance when exposed to high temperatures, as higher residual compressive strengths are reported for these mixtures compared to solely MK-based systems. Only slight differences in shrinkage behaviour are observed at temperatures of up to 600 °C with the inclusion of GBFS; however, slag-blended pastes exhibit enhanced stability at temperatures exceeding 800 °C, as no variation in the compressive strength and no additional shrinkage are identified. These results suggest that nanostructural modifications are induced in the gel by the inclusion of GBFS into MK-based geopolymers, improving the overall performance of these materials.
TL;DR: In this paper, the authors reviewed the literature related to the properties of fresh and hardened concrete published after the previous (12th) International Congress on the Chemistry of Cement held in Montreal in 2007.
TL;DR: The ability to create both porous and strong structures opens a new avenue for fabricating scaffolds for load-bearing bone defect repair and regeneration.
TL;DR: In this article, the properties of fly-ash-based geopolymer concrete (GPC) were studied using regression analysis to identify tendencies and correlations within the mechanical properties of GPC.
Abstract: The mechanical properties of fly-ash-based geopolymer concrete (GPC) were studied. Experimentally measured values of the static elastic modulus, Poisson’s ratio, compressive strength, and flexural strength of GPC specimens made from 25 fly ash (FA) stockpiles from different sources were recorded and analyzed. The results were studied using regression analysis to identify tendencies and correlations within the mechanical properties of GPC. It was found that the mechanical behavior of GPC is similar to that of ordinary portland cement (OPC) concrete, suggesting that equations, akin to those given by ACI 318-08, could be applied for GPC to determine its flexural strength and static elastic modulus. The validity of an equation to determine the density of GPC as a function of FA fineness was also put forward.
TL;DR: A series of simulations for hydraulic fracturing in competent rock was performed by using the flow-coupled DEM code to discuss the influence of the fluid viscosity and the particle size distribution as discussed by the authors.
TL;DR: Although multiple regression analysis was more accurate than Artificial neural network in predicting the compressive strength using values obtained from non-destructive testing, the artificial neural network models performed better than did multiple regressionAnalysis models.
Abstract: This study applies multiple regression analysis and an artificial neural network in estimating the compressive strength of concrete that contains various amounts of blast furnace slag and fly ash, based on the properties of the additives (blast furnace slag and fly ash in this case) and values obtained by non-destructive testing rebound number and ultrasonic pulse velocity for 28 different concrete mixtures (M"c"o"n"t"r"o"l and M"1-M"2"7) at different curing times (3, 7, 28, 90, and 180days). The results obtained using the two methods are then compared and discussed. The results reveal that although multiple regression analysis was more accurate than artificial neural network in predicting the compressive strength using values obtained from non-destructive testing, the artificial neural network models performed better than did multiple regression analysis models. The application of an artificial neural network to the prediction of the compressive strength in admixture concrete of various curing times shows great potential in terms of inverse problems, and it is suitable for calculating nonlinear functional relationships, for which classical methods cannot be applied.
TL;DR: In this paper, an analysis of fly ash paste morphology was performed using scanning electron microscopy (SEM/EDS) and microstructural properties with X-ray Diffraction (XRD) analysis.
Abstract: Fly ashes (FA) are byproducts of electricity production from mineral coal in thermoelectric power plants. The pozzolanic properties of FA have been utilized in various applications, including structural concrete, yet the large part of FA is still discarded into the environment. To promote greater FA usage, this study aims to produce a dense matrix, with mechanical properties satisfactory for civil engineering projects, from alkali-activated fly ash-based geopolymers. Three variables were studied: the Na2O/SiO2 molar ratio (N/S 0.20, N/S 0.30 and N/S 0.40); curing temperature in the first 24 h (50, 65 and 80 °C); and age (1, 7, 28, 91 and 180 days). For this study, alkali-activated fly ash pastes and mortars were prepared. In pastes, morphology was studied using scanning electron microscopy (SEM/EDS) and microstructural properties with X-ray Diffraction (XRD) analysis. Mortars were evaluated according to their mechanical performance measured using compression strength tests. Compression strength results were analysed using ANOVA. The results show that the N/S molar ratio plays an important role in the mechanical and morphological characteristics of geopolymers. The mortars prepared with a N/S 0.40 molar ratio had the greatest compression strength. The analysis of paste morphology revealed that N/S 0.40 pastes had a denser appearance, which is in agreement with results of compression strength tests.
TL;DR: In this paper, two different sources of recycled aggregates were used to replace natural aggregate at a level of 100%, and the compressive and splitting tensile strength of the concrete were tested, and the pore structures of concrete were analyzed.
Abstract: This paper presents the results of a study of the long term mechanical properties and pore structures of recycled aggregate concrete. In this study, two different sources of recycled aggregates were used to replace natural aggregate at a level of 100%. The compressive and splitting tensile strength of the concrete were tested, and the pore structures of the concrete were analyzed. The results showed that after 5 years of curing, the recycled aggregate concretes had lower compressive strength and higher splitting tensile strength than the corresponding natural aggregate concrete. However, from 28 days to 5 years, the increase of compressive and splitting tensile strengths was more in the recycled aggregate concretes. After 5 years of curing, the concrete made with 100% of crushed old concrete aggregate had the lowest porosity. Good correlations were found between compressive and tensile strength and porosity.
TL;DR: In this paper, the authors investigated the possibility of using Rice Husk Ash (RHA) to produce ultra high performance concrete (UHPC) and found that the compressive strength of UHPC incorporating RHA, with the mean size between 3.6μm and 9μm, can be achieved in excess of 150 MPa with normal curing regime.
TL;DR: In this article, the effect of temperature on thermal and mechanical properties of self-consolidating concrete (SCC) and fiber reinforced SCC (FRSCC) was presented. And the results showed that the presence of steel fibers enhances high temperature splitting tensile strength and elastic modulus of SCC.
TL;DR: In this article, the benefits of limestone powder (LP, basalt powder (BP) and marble powder (MP) as partial replacement of Portland cement are established, without attempting any additional processing in the production of self-compacting concrete (SCC).
Abstract: In this study, the benefits of limestone powder (LP), basalt powder (BP) and marble powder (MP) as partial replacement of Portland cement are established. Furthermore, LP, BP and MP are used directly without attempting any additional processing in the production of self-compacting concrete (SCC). The water to binder ratio is maintained at 0.33 for all mixtures. The examined properties include workability, air content, compressive strength, ultrasonic pulse velocity, and static and dynamic elastic moduli. Workability of the fresh concrete is determined by using both the slump-flow test and the L-box test. The results show that it is possible to successfully utilize waste LP, BP and MP as mineral admixtures in producing SCC. Due to its observed mechanical advantages, the employment of waste mineral admixtures improved the economical feasibility of SCC production on a unit strength basis.