Showing papers in "Cement and Concrete Research in 2008"

TL;DR: In this paper, the influence of the presence of limestone on the hydration of Portland cement was investigated, and it was shown that the stabilisation of monocarbonate in the absence of limestone indirectly stabilised ettringite, leading to a corresponding increase of the total volume of the hydrate phase and a decrease of porosity.

TL;DR: In this article, a number of models for the nanostructure of C-S-H are summarized and compared and it is shown that there is much more of a consensus than might seem apparent at first sight.

TL;DR: In this article, the authors argue that the cement and concrete industry is contributing positively to the Climate Change Initiative by: Continuously reducing the CO 2 emission from cement production by increased use of bio-fuels and alternative raw materials as well as introducing modified low-energy clinker types and cements with reduced clinker content.

TL;DR: In this article, the phase assemblage and pore solution of Portland cements hydrated between 0-60°C were modeled as a function of time and temperature, and a good correlation between calculated porosity and measured compressive strength was observed.

TL;DR: In this article, a second generation model for the nanostructure of C-S-H based on the interpretation of water sorption isotherms is presented, which can help to establish quantitative relationships between the nano-structural and bulk properties.

TL;DR: In this paper, the authors discuss the factors that have enabled these developments and ongoing needs in these areas and discuss the importance of sustainability as the major driver for future innovations and prospects for development of new cementitious materials with lower environmental impact.

TL;DR: In this paper, the mechanisms that govern the transport of ions, moisture, and gas are described, and different chemical degradation phenomena are reviewed, such as sulfate attack from external sources and formation of ettringite and thaumasite.

TL;DR: In this paper, the effects of bacterial carbonate precipitation (biodeposition) on the durability of mortar specimens with different porosity was assessed from the permeation properties and resistance towards degradation processes.

TL;DR: In this paper, the role of calcium in geopolymerisation was investigated and the effect of different calcium silicates on the performance of different matrices was found to depend most significantly on the crystallinity of the calcium silicate source and the alkalinity of activating solution used.

TL;DR: In this article, the nano-mechanical properties of the phases governing the UHPC microstructure were characterized by means of a novel statistical nanoindentation technique; then, those nanoscale properties were upscale to the macroscopic scale of engineering applications.

TL;DR: In this paper, the authors showed that the addition of small amounts of silica nanoparticles to the cement paste can induce a reduction in the degradation process of calcium leaching, which is a degradation process that consists in the progressive dissolution of the cement mixture as a consequence of the migration of the calcium ions to the aggressive solution.

TL;DR: In this article, the authors investigated the relationship between ASC hydration, unrestrained drying and autogenous shrinkage of mortar specimens and determined the chemical and microstructure evolution due to hydration.

TL;DR: In this paper, the effects of traversing cracks of concrete on chloride diffusion were examined, and three different concretes were tested: one ordinary concrete (OC), one high performance concrete (HPC and HPCSF), and two different mix designs with silica fume.

TL;DR: In this paper, the root-mean-squared (RMS) roughness of the sample, taken over a square area with edge dimensions of 200 times the average indentation depth of the dominating phase of the material, should be less than five times.

TL;DR: In this article, the effectiveness of internal curing (IC) to reduce autogenous shrinkage cracking in high performance concrete (HPC) was investigated using different levels of IC on four pairs of large-size prismatic HPC specimens tested simultaneously under free and restrained shrinkage.

TL;DR: A structural study of RHA samples in relation to their reactivity has been performed; Silica in RHA formed by burning rice husk in a laboratory furnace under continuous supply of air have been characterized as a function of incineration temperature, time and cooling regime as mentioned in this paper.

TL;DR: In this article, two possible strategies for tuning the mechanical properties of cementitious materials by modifying the bonding scheme in the hydrates at molecular level are discussed, based on the strengthening of the network of cohesion forces acting between the individual C-S-H lamellae or between their crystallites.

TL;DR: In this article, an overview of the early-age properties of cement-based materials from a materials science perspective is presented, where the major physical and chemical processes occurring at early ages are reviewed and strategies for mitigating early age cracking are presented.

TL;DR: In this article, the authors investigated the influence of the shape and size of the specimens on the compressive strength of high-strength concrete and found that the post-peak behavior of the cubes is milder than that of the cylinders, which results in a strong energy consumption after the peak.

TL;DR: In this article, the authors studied the behavior of suspensions of coarse particles in a thixotropic cement paste and showed that the yield stress of these suspensions with coarse particles follows the very simple Chateau-Ovarlez-Trung model with many different particles and suspending yield stress fluids.

TL;DR: In this article, the influence of a fine glass powder on cement hydration was investigated using flame emission spectroscopy and electrical conductivity tests to quantify the alkali release from glass powder.

TL;DR: In this article, an unsaturated poroelasticity theory is proposed to model the deformation of all the phases during the freezing process of concrete, and the analysis indicates that the air voids act both as expansion reservoirs and efficient cryo-pumps whose respective effects are quantitatively assessed.

TL;DR: In this paper, set cement samples are exposed to CO 2 fluids under pressure and temperature to simulate downhole conditions and quantified the bulk porosity evolution, as well as local porosity gradients through the samples, using combined mercury porosimetry and back-scattered electron image analysis.

TL;DR: In this article, the synthesis and performance of new methacrylate ester based polycarboxylate superplasticizers is compared to those of conventional ones, which possess hydroxy termination of the poly(ethylene glycol) side chains instead of conventional methoxy termination.

TL;DR: In this article, the effect of superplasticizers on the rheology of concrete and concrete has been investigated using both polycarboxylate and lignosulfonate polymers.

TL;DR: Shrinkage reducing admixtures (SRA) have been developed to combat shrinkage cracking in concrete elements as discussed by the authors, which has been shown to have significant benefits in reducing the magnitude of drying and autogenous shrinkage, however, SRA may cause a negative side effect as it reduces the rate of cement hydration and strength development.

TL;DR: In this article, the authors described the mechanical effects of rust layer formed in reinforced mortar through accelerated tests of corrosion, and the morphological and physico-chemical properties of the corrosion system were characterized at different stages by using optical microscope and scanning electron microscope coupled with energy dispersive spectroscopy.

TL;DR: In this article, the authors investigated the strength evolution of supersulphated cements produced by the activation of two different ground granulated blast furnace slags with anhydrite and small amounts of an alkaline activator.

TL;DR: The relationship between crack opening and chloride-ion diffusion along a crack is discussed in this paper, where it is shown that crack opening significantly affects chloride diffusion along the crack path and that self-healing could reduce chloride diffusion in cracks.

TL;DR: In this paper, the porosity development of fresh concrete was investigated using a noncontact electrical resistivity measurement, and the results showed that porosity change with time, which was caused by the increase of hydration products with a lower density as compared to that of the original cement in the hydration system.