A computed-based model for the alkali concentrations in pore solution of hydrating Portland cement paste

A computed-based model for the alkali concentrations in pore solution of hydrating Portland cement paste is proposed. Experimental data reported in different literatures with thirteen different recipes are analyzed. A 3-D computer-based cement hydration model CEMHYD3D is used to simulate the hydration of these pastes. The models predictions are used as inputs for the alkali partition theory, which is used to derive the alkali binding capacity of C-S-H in hydrating Portland cement paste. A linear relation between the amount of bound-alkali Na+ in C-S-H and its concentration in the pore solution is found, whilst a non-linear relation should be employed for the amount of bound-alkali K+ in C-S-H. New methods for predicting the alkali concentrations in the pore solution of hydrating Portland cement pastes are proposed based on the computer model CEMHYD3D, which is also validated with experimental results

Some Aspects of Low Content Mono- and Hybrid-Fibre Reinforced Cementitious Composites

Civil Engineering and Geoscience

Efficient reuse of the recycled construction waste cementitious materials

This paper addresses the efficiently reuse of the recycled construction waste cementitious materials (RCWCM). The RCWCM is firstly collected, and then subjected to crushing, grinding and thermal treatments, respectively. After that, the obtained powder material is named dehydrated cement paste (DCP) in this study. Due to the fact that the DCP has relatively high pH value and high activity, two specific attempts are tried to efficiently reuse the obtained DCP. The results show that it is possible to produce a prefabricated building material with an industry by-product (fly ash) and a recycled waste material (DCP). The compressive strength of the produced prefabricated building material can be higher than 60 MPa. Additionally, after being further dispersed, the DCP could be utilized as a high performance cement additive, which can significantly promote the hydration and microstructure development of cement

Efficient reuse of the recycled construction waste cementitious materials

This paper addresses the efficiently reuse of the recycled construction waste cementitious materials (RCWCM). The RCWCM is firstly collected, and then subjected to crushing, grinding and thermal treatments, respectively. After that, the obtained powder material is named dehydrated cement paste (DCP) in this study. Due to the fact that the DCP has relatively high pH value and high activity, two specific attempts are tried to efficiently reuse the obtained DCP. The results show that it is possible to produce a prefabricated building material with an industry by-product (fly ash) and a recycled waste material (DCP). The compressive strength of the produced prefabricated building material can be higher than 60 MPa. Additionally, after being further dispersed, the DCP could be utilized as a high performance cement additive, which can significantly promote the hydration and microstructure development of cement

Influence of agglomeration of a recycled cement additive on the hydration and microstructure development of cement based materials

This paper presents a study, including experimental and mechanism analysis, on investigating the effect of agglomeration of a recycled cement additive on the hydration and microstructure development of cement based materials. The recycled additive is firstly produced form waste hardened cement paste subjected to high temperature environment, namely original dehydrated cement paste (DCP). Then, to reduce the amount of agglomerated particles, the original DCP is dispersed by the method proposed in this study. The experimental results show that due to the agglomeration of the DCP particles, much free water can be trapped into the flaky layers, which cause that the cementitious system with original DCP need more water to maintain the normal consistency. Additionally, due to the nucleation effect of small DCP particles, the hydration and microstructure development of cement can be effectively promoted, which directly cause the enhancement of the mechanical properties of the cementitious system. However, this promotive effect of the fine particles in DCP could be obviously reduced by its particle agglomeration. (C) 2013 Elsevier Ltd. All rights reserved

Using dehydrated cement paste as new type of cement additive

This paper presents an experimental study, including evaluation and modification, on using dehydrated cement paste (DCP) as a new type of cement additive. After a series of processes, normal DCP (N-DCP) was produced as before and a modified form of DCP (M-DCP) was produced as well. The cementitious characteristics of the groups with different kinds and contents of DCPs were evaluated by following/using the required water of standard consistency, setting times, and compressive strength development. A new concept-evaluating the strength contribution of DCPs by using the theoretical strength contribution (TSC)-is proposed in this paper. The experimental results show that N-DCP can be used as a new type of cement additive to artificially adjust the consistency, setting times, and compressive strength of cement. When the content of N-DCP is approximately 9.47%, the value of TSC can reach 20% after approximately 1 day. In addition, the M-DCP that was produced in this study can be used to maintain high requirements of compressive strength in practice. Comparing that value of the N-DCP/cement system, when the content of M-DCP is approximately 3.5%, the value of TSC can reach almost 40% at both early and later stages

Three-dimensional computer modeling of slag cement hydration

A newly developed version of a three-dimensional computer model for simulating the hydration and microstructure development of slag cement pastes is presented in this study. It is based on a 3-D computer model for Portland cement hydration (CEMHYD3D) which was originally developed at NIST, taken over in the authors’ group and further developed. Features like the digitized 3-D microstructure, the cellular automata (CA) algorithm for simulating the random walking, phase transformation for simulating the chemical reactions, are retained. But, the 3-D microstructure was reconstructed allowing for slag particles as binder in the system. Algorithms and rules are developed to account for the interaction between Portland cement hydration and slag reaction in the paste, of which the mechanisms were revealed in the studies by Chen and Brouwers [(2007) J Mater Sci 42(2):428; (2007) J Mater Sci 42(2):444] Methods for considering the various factors on the reactivity of slag in hydrating slag cement pastes are proposed, mainly for the oxide composition of slag and the alkalinity in the pore solution composition. A comparison between the model predictions and the experimental results in literature shows that the presented computer model can successfully predict the hydration process and the microstructure development of hydrating slag cement paste

A computed-based model for the alkali concentrations in pore solution of hydrating Portland cement paste

A computed-based model for the alkali concentrations in pore solution of hydrating Portland cement paste is proposed. Experimental data reported in different literatures with thirteen different recipes are analyzed.A3-D computer-based cement hydration modelCEMHYD3Dis used to simulate the hydration of these pastes. The models predictions are used as inputs for the alkali partition theory, which is used to derive the alkali binding capacity of C-S-H in hydrating Portland cement paste. A linear relation between the amount of boundalkali Na+ in C-S-H and its concentration in the pore solution is found, whilst a non-linear relation should be employed for the amount of bound-alkali K+ in C-S-H. New methods for predicting the alkali concentrations in the pore solution of hydrating Portland cement pastes are proposed based on the computer model CEMHYD3D, which is also validated with experimental results