Cement

About: Cement is a research topic. Over the lifetime, 68440 publications have been published within this topic receiving 829356 citations.

Autogenous Deformation and Internal Curing of Concrete

Abstract: High-performance concrete (HPC) is generally characterized by a low water/binder ratio and by silica-fume addition, which guarantee a low porosity and a discontinuous capillary pore structure of the cement paste. Modern concretes possess some highly advantageous properties compared to traditional concrete, such as good workability in the fresh state, high strength, and low permeability. However, they have also shown to be more sensitive to early-age cracking than traditional concrete. Early-age cracking mainly occurs due to the fact that the deformations of the concrete member are restrained by adjoining structures. In addition, internal microcracking may occur, due to restraint offered to the shrinking paste by the non-shrinking aggregates. A main source of early-age deformations in HPC is autogenous deformation. Autogenous deformation is the self-created deformation of a cement paste, mortar or concrete during hardening. In traditional concretes it is negligible compared to drying shrinkage. However, the low water/binder ratio and the addition of silica fume in HPC cause a significant drop of the internal relative humidity (RH) in the cement paste during sealed hydration and the occurrence of autogenous shrinkage. Despite the growing interest in autogenous shrinkage, no consensus has been reached in the scientific community about its mechanisms neither about measuring methods. Moreover, different strategies aimed at limiting the autogenous shrinkage are debated at the moment. In this thesis, autogenous deformation of cement pastes, Normal Weight Concrete (NWC), and Lightweight Aggregate Concrete (LWAC) were measured. Both Portland and Blast Furnace Slag (BFS) cement were studied. A model for calculating self-desiccation shrinkage of cement paste was proposed and validated with experiments. Shrinkage of NWC was derived with a composite model and early-age expansion of LWAC, a puzzling phenomenon up to now, was explained. Finally, transport of water from saturated lightweight aggregates (LWA) to hardening cement paste was measured with x-ray absorption.

Dentin-cement Interfacial Interaction: Calcium Silicates and Polyalkenoates

Abstract: The interfacial properties of a new calcium-silicate-based coronal restorative material (Biodentine™) and a glass-ionomer cement (GIC) with dentin have been studied by confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), micro-Raman spectroscopy, and two-photon auto-fluorescence and second-harmonic-generation (SHG) imaging. Results indicate the formation of tag-like structures alongside an interfacial layer called the "mineral infiltration zone", where the alkaline caustic effect of the calcium silicate cement's hydration products degrades the collagenous component of the interfacial dentin. This degradation leads to the formation of a porous structure which facilitates the permeation of high concentrations of Ca(2+), OH(-), and CO(3) (2-) ions, leading to increased mineralization in this region. Comparison of the dentin-restorative interfaces shows that there is a dentin-mineral infiltration with the Biodentine, whereas polyacrylic and tartaric acids and their salts characterize the penetration of the GIC. A new type of interfacial interaction, "the mineral infiltration zone", is suggested for these calcium-silicate-based cements.

Strength and modulus of marine clay-cement mixes

Abstract: This paper examines the strength and modulus of marine clay-cement mixes with high cement content. Although similar studies have been reported, many of these studies were conducted using soil-cement and water-cement ratios which are more applicable to deep cement mixing than jet grouting. The objective of this study is to investigate how the strength and modulus of cement-treated Singapore marine clay vary with cement and water contents at a range of cement contents, which is more representative of that used in jet grouting. To facilitate parametric studies that are relevant to jet grouting operations, a working range of the constituents was proposed for Singapore marine clay based on the liquid and bleeding limits of the soil-cement mixes. Comparison with data from some previous jet grouting studies and projects indicates that the liquid and bleeding limits can encompass most, if not all, of the parameter range normally used in jet grouting operations. The results of unconfined compression tests on cemen...