Showing papers in "Cement & Concrete Composites in 2004"
TL;DR: In this article, the general microstructural features of hydrated cement pastes are described and the possibilities to quantify backscattered electron imaging images of polished surfaces are described. And an example of the potential for BSE images to study concrete durability is given.
Abstract: During the last 20 years, backscattered electron imaging of polished surfaces has become well established as a method for the study of cement and concrete microstructures. The technique has many advantages, including the visualisation of representative cross-sections over a wide range of magnifications and reproducible contrast dependent on atomic number. Nevertheless the limitations of observing a two-dimensional section of a three-dimensional structure must be borne in mind. In this paper, the general microstructural features of hydrated cement pastes are described. Although the amount of aluminate phase ("C3A") in cement is comparatively minor, it plays an important role in determining many of the microstructural features of cement paste microstructure, for example in the formation of "Hadley" grains. Despite the very heterogeneous nature of cement paste, it is important to be able to derive quantitative measures if the relationships between microstructure and properties are to be understood. The possibilities to quantify BSE images are described. The interface between paste and aggregates in concrete is particularly variable, but average features can be measured, which help to understand the processes of packing cement grains, which gives rise to this region. Finally an example of the potential for BSE images to study concrete durability is given. © 2004 Elsevier Ltd. All rights reserved.
702 citations
TL;DR: In this paper, the effects of binder systems containing different levels of silica fume on fresh and mechanical properties of concrete were investigated, and the results indicated that as the proportion of fume increased, the workability of concrete decreased but its short-term mechanical properties such as 28-day compressive strength and secant modulus improved.
Abstract: This paper presents the results of experimental work on short- and long-term mechanical properties of high-strength concrete containing different levels of silica fume. The aim of the study was to investigate the effects of binder systems containing different levels of silica fume on fresh and mechanical properties of concrete. The work focused on concrete mixes having a fixed water/binder ratio of 0.35 and a constant total binder content of 500 kg/m3. The percentages of silica fume that replaced cement in this research were: 0%, 6%, 10% and 15%. Apart from measuring the workability of fresh concrete, the mechanical properties evaluated were: development of compressive strength; secant modulus of elasticity; strain due to creep, shrinkage, swelling and moisture movement. The results of this research indicate that as the proportion of silica fume increased, the workability of concrete decreased but its short-term mechanical properties such as 28-day compressive strength and secant modulus improved. Also the percentages of silica fume replacement did not have a significant influence on total shrinkage; however, the autogenous shrinkage of concrete increased as the amount of silica fume increased. Moreover, the basic creep of concrete decreased at higher silica fume replacement levels. Drying creep (total creep − basic creep) of specimens was negligible in this investigation. The results of swelling tests after shrinkage and creep indicate that increasing the proportion of silica fume lowered the amount of expansion. Because the existing models for predicting creep and shrinkage were inaccurate for high-strength concrete containing silica fume, alternative prediction models are presented here.
531 citations
TL;DR: In this paper, the authors report on the Algerian experience on earth construction in housing and give an extended review of an experimental study to investigate a stabilised soil by either mechanical means such as compaction and vibration and/or chemical stabilisation by cement.
Abstract: Earth construction is widespread in desert and rural areas because of its abundance and cheap labour and could be an alternative construction material for low cost housing in Algeria. However, earth construction suffers from shrinkage cracking, low strength and lack of durability. This paper reports on the Algerian experience on earth construction in housing and gives an extended review of an experimental study to investigate a stabilised soil by either mechanical means such as compaction and vibration and/or chemical stabilisation by cement. Soil used was characterised by its grading curve and chemical composition. Compaction was either applied statically or dynamically by a drop weight method. A mixture of sand and cement was also tried. The effect of each method of stabilisation on shrinkage, compressive strength, splitting tensile strength and water resistance are briefly reported. The experimental results showed that the best method of stabilisation of the soil investigated, which gives a good compressive strength and a better durability at a reasonable cost, could be a combination of a mechanical compaction and chemical stabilisation by cement or sand and cement up to a certain level.
313 citations
TL;DR: In this article, the authors presented the conductive behavior of carbon fiber cement-based composites and the relationship between conductivity and volume fraction of carbon fibre indicated that the statistical percolation theory is suitable and applicable for the change rule of conductivity of system with the volume of the carbon fiber.
Abstract: The conductive behavior of carbon fiber cement-based composites is presented. The influence of carbon fiber volume, size, cement-based matrix, relative humidity and curing age on the characteristic of system were studied. The relationship between conductivity and volume fraction of carbon fiber indicated that the statistical percolation theory is suitable and applicable for the change rule of conductivity of system with the volume of carbon fiber. Based on the classic percolation theory, the percolation threshold of carbon fiber cement-based composites was determined as φ=φc2 and the conductive mechanism changes from electron tunneling conduction to ohmic contacting conduction. The studies have offered basic theory for smart cement-based composites.
305 citations
TL;DR: In this article, a general overview of recent developments in the study of the fatigue behavior of plain and fiber reinforced concrete (FRC) is provided in order to quantify the influence of fibre inclusion on fatigue behavior.
Abstract: The paper provides a general overview of recent developments in the study of the fatigue behaviour of plain and fibre reinforced concrete (FRC). The fatigue performance of plain concrete and FRC, as reported in the literature, is compared in order to quantify the influence of fibre inclusion on fatigue behaviour. Despite the conflicting information regarding the fatigue behaviour of concrete reported in the literature, the majority of researchers show that the inclusion of fibres can benefit the fatigue performance of concrete.
303 citations
TL;DR: In this paper, the authors present a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage in concrete, including the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of the concrete, addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of water-entrained concrete.
Abstract: As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper, the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore network, the visco-elastic response of the developing solid framework, and the kinetics of the cementitious reactions. While the complexity of this phenomenon may hinder a quantitative interpretation of a specific cement-based system, it also offers a wide variety of possible solutions to the problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of the cement, the addition of saturated lightweight fine aggregates, the use of controlled permeability formwork, and the new concept of “water-entrained” concrete. As with any remedy, new problems may be created by the application of each of these strategies. But, with careful attention to detail in the field, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches.
285 citations
TL;DR: In this paper, the microstructure of hardened cement paste and paste in concrete is shown in backscattermode scanning electron microscopy (SEM) and illustrated with an image.
Abstract: This paper represents an attempt to provide an introduction to the microstructure of cement paste and concrete as seen in backscatter-mode scanning electron microscopy (SEM). Illustrations are provided of the `internal architecture' underlying the microstructure of hardened cement paste and paste in concrete, at the size scales accessible to this instrument. Concrete is a uniquely complex engineering material. The aim of this paper is to provide researchers and practitioners who deal with it an acquaintance with its internal structure.
270 citations
TL;DR: In this paper, an analytical stress formulation is presented to compute the actual residual stress level in the concrete using only the measured strain from the steel ring, and a comparison of the residual and theoretical elastic stress levels provides information about the extent of stress relaxation in a material.
Abstract: Recently, the American Association of State Highway and Transportation Officials implemented a provisional standard that uses the `ring test' to help quantify a materials' propensity for cracking. While this test may provide qualitative information that enables different mixtures to be compared, it does not provide quantitative information to describe how close a specimen is to failure. This paper will describe how the ring test may be used to provide quantitative information about stress development that may be used to assess the potential for cracking in concrete. An analytical stress formulation is presented to compute the actual residual stress level in the concrete using only the measured strain from the steel ring. The theoretical elastic stress is computed using the free shrinkage, ring deformation, and elastic modulus of the concrete. A comparison of the residual and theoretical elastic stress levels provides information about the extent of stress relaxation in a material. Continuously monitoring the strain that develops in the steel ring from the time of casting enables the effects of autogenous shrinkage to be determined as well as the effects of drying shrinkage.
266 citations
TL;DR: In this article, the authors present the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads.
Abstract: This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load–deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural parameters on the load carrying capacity and the post-peak behaviour of the beam. In particular, the results show that the inclusion of fibres in adequate percentage can change the brittle mode of failure characterizing shear collapse into a ductile flexural mechanism, confirming the possibility of achieving analogous performance by using reinforcing fibres instead of increasing the amount of transverse reinforcement. The ultimate values of the shear stresses recorded experimentally are compared with the corresponding values deduced by semiempirical expressions available in the literature and the correlation is satisfactory.
249 citations
TL;DR: In this article, an experimental study on the optimum amount of polypropylene fibres to be used in lightweight high-strength concrete to prevent spalling when exposed to hydrocarbon fire, taking into consideration the characteristics of the lightweight aggregate, the water-to-cement ratio (W/C) of the mixtures, and the length and thickness of the fibres.
Abstract: This paper presents the results from an experimental study on the optimum amount of polypropylene fibres to be used in lightweight high-strength concrete to prevent spalling when exposed to hydrocarbon fire, taking into consideration the characteristics of the lightweight aggregate, the water-to-cement ratio (W/C) of the mixtures, and the length and thickness of the fibres. Twelve different concrete mixtures were made. One block, 610 × 425 × 770 mm in size, was cast from each mixture and tested for fire resistance under hydrocarbon fire exposure. The temperature in the blocks during the test was recorded. After the test, the condition of the blocks was evaluated, and cores were taken for determining the residual compressive strength of the concrete. Results from the study show that close to 3.5 kg of the 20-mm polypropylene fibres per cubic meter of concrete is required to prevent the spalling of a low W/C lightweight concrete made with a silica fume-blended cement when subjected to hydrocarbon fire but that only 1.5 kg of the finer 12.5-mm fibres per cubic meter is sufficient. The amount of 20-mm fibres required to prevent spalling for a higher W/C of 0.42 is significantly less: of the order of 1.5 kg per cubic meter of concrete. The susceptibility of the concrete to spalling increases with the degree of absorption of the lightweight aggregate used in concrete.
224 citations
TL;DR: In this article, a Finnish test arrangement has been used to measure linear and volumetric deformations of concrete immediately after mixing, and the slabs are tested in either drying or autogenous conditions.
Abstract: When assessing the cracking potential of concrete it is critical to refer to the total shrinkage: both early age and long-term deformation, in both drying and autogenous conditions. A Finnish test arrangement has been used to measure linear and volumetric deformations of concrete immediately after mixing. The slabs are tested in either drying or autogenous conditions. Long-term shrinkage can be measured on the same slabs to give an accurate representation of the total free shrinkage. From these measurements it is possible to assess the likelihood of cracking due to early age shrinkage. Results have shown that both drying and autogenous shrinkage can be significant in certain early age scenarios. Environmental factors greatly affect drying shrinkage, while material properties affect autogenous shrinkage. This paper provides insight regarding how to interpret early age deformations, how environmental and material factors play a role, and how to minimize shrinkage and thus cracking potential in the early ages.
TL;DR: In this article, the chemical reactions of the corrosion process in concrete and of the most commonly used inhibitors are discussed, with special attention to test procedures and practical issues arising from use of inhibitors.
Abstract: In the last quarter century, it has become feasible to extend the life of reinforced concrete structures by inhibiting chloride-induced corrosion of steel. Chemical interactions can occur between the concrete system and the inhibitor-steel-chloride system. The chemical reactions of the corrosion process in concrete and of the most commonly used inhibitors are discussed, with special attention to test procedures and practical issues arising from use of inhibitors.
TL;DR: In this paper, a numerical model, in the form of a computer program, for tracing the behavior of high performance concrete (HPC) columns exposed to fire is presented. But the model is limited to the case of HPC columns and cannot be used to predict the fire resistance of any value of the significant parameters, such as load, section dimensions, fiber reinforcement, column length, concrete strength, aggregate type, and fiber reinforcement.
Abstract: A numerical model, in the form of a computer program, for tracing the behaviour of high performance concrete (HPC) columns exposed to fire is presented. The three stages, associated with the thermal and structural analysis, for the calculation of fire resistance of columns are explained. A simplified approach is proposed to account for spalling under fire conditions. The use of the computer program for tracing the response of an HPC column from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in the program is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Details of fire resistance experiments carried out on HPC columns, together with results, are presented. The computer program can be used to predict the fire resistance of HPC columns for any value of the significant parameters, such as load, section dimensions, fiber reinforcement, column length, concrete strength, aggregate type, and fiber reinforcement.
TL;DR: In this article, the effects of coarse aggregate size and water/cement ratio of the matrix on the formation of interfacial transition zone (ITZ) and subsequently on the failure process of concrete under uniaxial compression were studied.
Abstract: Effects of coarse aggregate size and water/cement (w/c) ratio of the matrix on the formation of interfacial transition zone (ITZ) and subsequently on the failure process of concrete under uniaxial compression were studied. For this purpose, a series of experiments were designed and carried out on mortars with two different w/c ratios containing single spherical steel aggregates of different sizes. The ITZ properties and the failure process of concrete were investigated through tensile strength tests both before and after compressive preloading, stress-axial strain, stress-volumetric strain and stress-lateral strain measurements. It was observed that ITZ becomes critical for larger aggregates and lower w/c ratio mortar matrices. The negative effect of smooth surface texture of the aggregate and the large difference between aggregate and matrix moduli of elasticity on the properties of ITZ is of paramount importance for low w/c ratio composites. The effect of reduced bond properties of ITZ relative to its matrix was reflected in the lower critical stress levels for the low w/c ratio composites with larger aggregates. (A) "Reprinted with permission from Elsevier".
TL;DR: In this article, two lightweight aggregate concretes, SLWC35 and SLWC50, of 35 and 50 MPa 28 day cube compressive strength were cast, and they were continuously cured in water for one or seven days and then exposed to predominantly hot and humid seaside ambient conditions containing airborne salts.
Abstract: Two lightweight aggregate concretes, SLWC35 and SLWC50, of 35 and 50 MPa 28 day cube compressive strength were cast. The concrete specimens made with lightweight coarse aggregates and a dune sand were continuously cured in water for one or 7 days and then exposed to predominantly hot and humid seaside ambient conditions containing air-borne salts. After 7 days of initial curing and on subsequent exposure to hot and humid air both SLWCs attained an almost similar strength to those continuously water cured cubes at an age of 12 months. In contrast, the water penetrability of SLWC35 and SLWC50 after 7 days of initial curing and subsequent exposure to the sea side was about 2 and 1.8 times the water penetration of those slabs which were water cured for the entire duration of 12 months. However, the depth of carbonation of the two sand lightweight concretes up to an age of 12 months were negligibly small. The results suggest that compressive strength is comparatively less sensitive to the curing regimes investigated. Both the chloride and sulphate penetration after 12 months exposure were found to be within tolerable limits. Also replacement of lightweight fine aggregate with normal weight sand produces a concrete that is somewhat more durable as indicated by their water penetrability and depth of carbonation when concretes are of equal strength.
TL;DR: In this article, the authors present test results at failure of 16 reinforced concrete (RC) continuous beams with different arrangements of internal steel bars and external carbon fibre reinforced polymer (CFRP) laminates.
Abstract: This paper presents test results at failure of 16 reinforced concrete (RC) continuous beams with different arrangements of internal steel bars and external carbon fibre reinforced polymer (CFRP) laminates. All test specimens had the same geometrical dimensions and were classified into three groups according to the amount of internal steel reinforcement. Each group included one unstrengthened control beam designed to fail in flexure. Different parameters including the length, thickness, position and form of the CFRP laminates were investigated. Three failure modes of beams with external CFRP laminates were observed, namely laminate rupture, laminate separation and peeling failure of the concrete cover attached to the laminate. The ductility of all strengthened beams was reduced compared with that of the respective unstrengthened control beam. Simplified methods for estimating the flexural load capacity and the interface shear stresses between the adhesive and concrete at failure of beams tested are presented. Comparisons between results from experiments and those obtained from the simplified methods show that most beams were close to achieving their full flexural capacity and the longitudinal elastic shear stresses at the adhesive/concrete interface calculated at beam failure conformed to the limiting value recommended in the Concrete Society Technical Report 55.
TL;DR: In this article, the effects of the aspect ratio (L/d) and volume fraction of steel fiber reinforced concretes on fracture properties of concrete in bending were investigated by measuring the fracture energy and characteristic length.
Abstract: The objective of this research is to optimise the fracture parameters of steel fibre reinforced concretes to obtain a more ductile behaviour than that of plain concrete. The effects of the aspect ratio (L/d) and volume fraction of steel fibre (Vf) on fracture properties of concrete in bending were investigated by measuring the fracture energy (GF) and characteristic length (lch). For optimisation, three-level full factorial experimental design and response surface method were used. The results show that the effects of fibre volume fraction and aspect ratio on fracture energy and characteristic length are very significant.
TL;DR: In this article, a nonlinear finite element approach is adopted for tracing the spatial and temporal advancement of the carbonation front in concrete structures with and without cracks, and the results obtained from the program are compared with available experimental data.
Abstract: Carbonation is one of the many reasons of reinforcement corrosion in concrete structures. Due to the coupling effects of moisture, heat and carbon dioxide transport in concrete, the modeling of this problem is a rather challenging task. A nonlinear finite element approach is adopted here for tracing the spatial and temporal advancement of the carbonation front in concrete structures with and without cracks. A two-dimensional Windows-based finite element computer program, called CONDUR, is developed and the results obtained from the program are compared with available experimental data. The program is designed to be flexible and comprehensive in its scope.
TL;DR: In this article, steel reinforced 100×100×300 mm concrete prisms, with nominal strength grades C25, C35 and C45 and different pfa levels (0-50%), were exposed to various curing treatments during the first 28 days prior to exposure in the tidal zone of the BRE marine exposure site.
Abstract: Steel reinforced 100×100×300 mm concrete prisms, with nominal strength grades C25, C35 and C45 and different pfa levels (0–50%), were exposed to various curing treatments during the first 28 days prior to exposure in the tidal zone of the BRE marine exposure site. Chloride concentration profiles and rebar weight losses had previously been measured on specimens exposed for 1, 2 and 4 years and this paper reports the results of similar measurements after 10 years exposure. Chloride profiles were also measured for specimens after 1 and 28 days immersion in seawater under laboratory conditions. Pfa concretes showed substantially increased resistance to the penetration of chlorides compared with control Portland cement (PC) concrete specimens. The improved resistance of the pfa concrete to the penetration of chlorides resulted in reduced corrosion of steel bars imbedded in the concrete. Threshold chloride levels for corrosion, estimated from relationships between steel weight loss and chloride content at the location of the steel, were found to decrease with increasing pfa content. Chloride concentration profiles after 28 days of immersion in seawater showed that considerable chloride penetration occurred during this period due to sorption (capillary suction) of the seawater into the unsaturated specimens. This results in a significant error in diffusion coefficients calculated from the concentration profile using the standard solution to Fick’s second law. The error may be substantial for pfa concretes where chlorides penetrating due to sorption immediately after exposure may outweigh subsequent diffusion during continued seawater exposure. The performance of the concretes, particularly the PC concretes, in this programme is considered in the light of current and new British Standard recommendations for concrete exposed to marine tidal conditions. The adequacy of these recommendations is, however, difficult to assess because the highest concrete quality tested fell a little short of the minimum quality required in the recommendations and cover to reinforcement was also less than required. Nevertheless, the superior performance of concretes containing 30% or more pfa was clearly demonstrated.
TL;DR: In this article, the authors used the scanning electron microscope (SEM) with X-ray microanalysis to study clinker and cements; permitting measuring bulk phase abundance and surface areas of the phases, as well as bulk chemistry of constituent phases.
Abstract: Use of the scanning electron microscope (SEM) with X-ray microanalysis allows study of clinker and cements; permitting measuring bulk phase abundance and surface areas of the phases, as well as bulk chemistry of constituent phases can be carried out. Direct imaging of hydraulic cements by SEM yields a more complete picture of both bulk and surface phase compositions. Mass percentages obtained by SEM imaging are in good agreement with percentages based upon QXRD and may differ significantly from those estimated by the Bogue calculations. The finer-grained phases (gypsum, tricalcium aluminate, and ferrite) show much higher surface areas per unit mass than the coarser-grained phases such as alite and belite. Such data are being applied to develop better relationships between the cement material properties and performance properties and to provide starting images for a cement hydration simulation model being developed at NIST.
TL;DR: In this paper, a random lattice is used to model moisture transport in cement-based composites, and the scaling of the elemental diffusivity terms are based on a Voronoi discretization of the material domain.
Abstract: A random lattice is used to model moisture transport in cement-based composites. Model geometry, and the scaling of the elemental diffusivity terms, are based on a Voronoi discretization of the material domain. Steady-state and transient potential flow problems are simulated, and compared with theory, to demonstrate model accuracy and objectivity with respect to lattice random geometry. A novel routine is described for computing moisture flux values at the random lattice sites. Stress production, and potential shrinkage crack development, are driven by the associated drying processes. The random lattice modeling of moisture movement is coupled with rigid-body-spring networks (RBSN), which account for elasticity, creep, and fracture properties of the material. The RBSN is based on the same Voronoi discretization of the material as used to model moisture movement. Relative humidity contours, stress contours, and crack plots are produced for a cement composite overlay restrained by a mature concrete substrate. That example is based on a set of simulation results reported in the literature.
TL;DR: In this paper, the formation of microstructure in cementitious materials was simulated with a numerical model and the simulation results have been verified by measuring the evolution of the ultrasonic pulse velocity (UPV).
Abstract: The formation of microstructure in cementitious materials was simulated with a numerical model. Simulation results have been verified by measuring the evolution of the ultrasonic pulse velocity (UPV). In this contribution, the applied computer-based cement hydration model is presented. The UPV measurements are also presented and evaluated. Experiments were performed on concrete mixtures with water/cement ratio 0.40, 0.45 and 0.55. The concrete was cured isothermally at 10, 20, 30 and 40 °C. Correlations between the development of the microstructure and the evolution of UPV were found. Two critical processes were individuated. The first is the percolation threshold of the solid phase. The second is the full connectivity of the solid phase. Both in the experiments and in the numerical simulations it was possible to distinguish these critical stages. These stages are discussed and conclusions are drawn regarding the potential of numerical simulation models in the study of early age cementitious materials for quantitative analysis of hydration processes.
TL;DR: In this article, the pastes of neat and blended Portland cement (incorporating either 60% ground granulated blast furnace slag, or 30% pulverised fuel ash, or 22% volcanic ash) were cured for one year at temperatures ranging from 10 to 60 °C.
Abstract: Pastes of neat and blended Portland cement (incorporating either 60% ground granulated blast furnace slag, or 30% pulverised fuel ash, or 22% volcanic ash) were cured for one year at temperatures ranging from 10 to 60 °C. The hydration products were characterised by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The apparent porosity of the pastes increased with increasing curing temperature. Chemical analysis data for the hydration products are presented in ternary composition diagrams, where it is noted that in the presence of the replacement materials the composition of the C–S–H shifted towards higher Si and Al contents, whereas that of Ca was lower.
TL;DR: In this article, the effect of tire rubber ash (TRA) filler on different properties of Portland cement mortar was investigated, including air content, setting time, compressive and flexural strength, freezing and thawing damage, and chloride-ion penetration.
Abstract: The present study explores the effect of tire rubber ash (TRA) filler on different properties of Portland cement mortar. The properties investigated include air content, setting time, compressive and flexural strength, freezing and thawing damage, and chloride-ion penetration. The TRA was obtained by incinerating bulk quantities of tire rubber chips in an oven at a controlled temperature of 850 °C for 72 h. The TRA filler was utilized as partial replacement of sand in mortar mixtures at four levels: 2.5%, 5%, 7.5%, and 10% by weight. The water to cementitious materials ratio used in the mortar mixtures was 0.65. The test results showed that TRA could be used as a partial replacement of sand in mortar mixtures to produce workable mortar. The air content of the fresh mortar decreased with increasing TRA content. The initial and final setting time of fresh paste increased with increasing TRA content. The mortar containing different TRA replacement levels showed higher compressive strength at various curing periods up to the age of 90 days compared with control mortar. Also, the flexural strength of the TRA mortar was higher than that of control mortar. The mortar containing 5% and 10% TRA showed higher resistance to freezing and thawing damage and chloride-ion penetration than that of control mortar.
TL;DR: In this article, an experimental program on compressive strength, porosity, electrical resistivity and polarization curves was carried out with the purpose of evaluating the effect of different silica fume (SF) additions (0, 6% and 12%).
Abstract: The addition of silica fume (SF) in concretes has been proposed as a form to improve their performance in resisting concrete reinforcement corrosion. In this study an experimental program on compressive strength, porosity, electrical resistivity and polarization curves was carried out with the purpose of evaluating the effect of different SF additions (0%, 6% and 12%). Concretes with different water–binder ratio (cement + SF) 0.50, 0.65 and 0.80 were used. The results have allowed to show that there are significant improvements of the concrete properties with the SF addition, suggesting its use in aggressive environments.
TL;DR: In this article, the levels of chloride to which given levels of calcium nitrite will protect steel reinforced concrete from chloride induced corrosion is analyzed and it is shown that once corrosion initiates, the rates are lower with calcium Nitrite present.
Abstract: Steel reinforced concrete is one of the most durable and cost effective construction materials, but it can suffer in high chloride environments from corrosion due to chloride induced breakdown of the normal passive layer protecting the steel. One way of protecting embedded steel reinforcement from chloride induced corrosion is by the addition of corrosion inhibiting admixtures. The most widely used corrosion inhibiting admixture is calcium nitrite, due to its excellent inhibitor properties and its benign effect on concrete properties. One advantage to calcium nitrite is that its protection mechanism is well defined. In this paper data are presented that show the levels of chloride to which given levels of calcium nitrite will protect. Furthermore, it will be shown that once corrosion initiates, the rates are lower with calcium nitrite present. Finally, it is demonstrated how these results can be used by the design engineer in an integrated durability model to produce reinforced concrete structures with durabilities in excess of 50–100 years.
TL;DR: In this paper, the formation of microstructure in cement pastes and mortars was quantitatively analyzed by the SEM-BSE image analysis effects of water/cement ratio and of the addition of mineral admixtures on the contents of unhydrated cement particles and pores were discussed The proportions obtained by the analyses were compared with proportions calculated on the Powers model.
Abstract: Formation of microstructure in cement pastes and mortars were quantitatively analyzed by the SEM-BSE image analysis Effects of water/cement ratio and of the addition of mineral admixtures on the contents of unhydrated cement particles and pores were discussed The proportions of each phase obtained by the analyses were compared with proportions calculated on the Powers model It was found from comparisons that the volume fractions of the residual cement and pores obtained by the image analysis did not contradict those estimated from the Powers model Lower water/cement ratio pastes and those undergoing pozzolanic reaction showed less fine capillary pores It was also found that large capillary pores still remained in the mixtures at long ages The gel/space ratio in the Powers and Brownyard equation was calculated from the phase constituents determined by the image analysis For mortars without mineral admixture, the gel/space ratio by the image analysis could be related to the strength
TL;DR: In this paper, the effects of styrene-butadiene rubber latex (SBR) modification on the durability of lightweight concrete (LWAC) were investigated and compared with the unmodified LWAC.
Abstract: The effects of styrene–butadiene rubber latex (SBR) modification on the durability of lightweight concrete (LWAC) were investigated. Corrosion resistance, chemical resistance and water absorption of SBR-modified LWAC were analyzed and compared with the unmodified LWAC. The 7-day compressive strength as well as the dry concrete density varied from 39.5 to 51.9 MPa and from 1460 to 1605 kg/m3, respectively. The results of this study demonstrate that the performance of SBR-modified LWAC exposed to aggressive environments was better than unmodified one. SBR-modified LWAC led to lower water absorption and significant resistance improvement to chemical attack and corrosion.
TL;DR: In this article, the effect of the properties of the cement paste matrix on the effectiveness of internal curing is discussed in this paper, and the authors also studied the effect that grain size, pore structure and type of the lightweight aggregate was studied.
Abstract: A novel approach to has been recently proposed mitigate self-desiccation, one of the foremost problems of high-performance concrete (HPC). It is based on incorporation of pre-soaked lightweight aggregate in the concrete mix. Such aggregate acts as an internal water reservoir preventing reduction of relative humidity in the cementitious matrix. This method is known as “autogenous” or “internal” curing. Recent studies demonstrated that this kind of curing could be successfully applied to obtain improved HPC with reduced sensitivity to cracking. However, the content of lightweight aggregate required to completely eliminate autogenous shrinkage was high, and this caused a reduction of compressive strength and an increase in the cost of the concrete. Recently, a work has been conducted to optimize the internal curing strategy by eliminating autogenous shrinkage while using the smallest possible amount of lightweight aggregate. The effect of grain size, pore structure and type of the lightweight aggregate was studied. The next step in this study––the effect of the properties of the cement paste matrix on the effectiveness of internal curing is discussed in this paper.
TL;DR: In this article, the multi-functional benefits of the water-based organic corrosion inhibitor are presented and discussed, with regard to the corrosion protection of embedded steel and resistance to chemical attack; specifically the resistance of concrete to sulfate attack and deterioration due to sulfuric acid exposure.
Abstract: In this paper, the multi-functional benefits of the water-based organic corrosion inhibitor are presented and discussed, with regard to the corrosion protection of embedded steel and resistance to chemical attack; specifically, the resistance of concrete to sulfate attack and deterioration due to sulfuric acid exposure. The organic corrosion inhibitor consists of amines and fatty-acid esters and the mechanisms by which it functions are presented and substantiated. In addition to a 30% of calcium nitrite inhibitor, this amine-ester based organic corrosion inhibitor is a commonly used corrosion inhibitor in new construction. Time-to-corrosion evaluations in 0.50 and 0.40 water-cementitious materials ratio concretes of moderate and high quality show that the inhibitor was effective regardless of concrete quality, and significantly reduced chloride ingress. The permeability-reducing property of the amine-ester based organic corrosion inhibitor has also shown effectiveness in reducing deterioration due to the ingress of other aggressive species such as sulfate and sulfuric acid. For comparison purposes, the corrosion-inhibiting performance of the amine-ester based organic inhibitor is compared to that of calcium nitrite, while its effect in mitigating sulfate attack and reducing deterioration due to sulfuric acid exposure is compared to that of silica fume.