424 publications from this institution
Modeling the hydration and the development of microstructure of blended cement are different in comparing with Portland cement due to the complex of the reactants, the hydration products and their interactions in the blended system. In this study, the hydration and microstructural formation of Portland cement blended with blast furnace slag are simulated based on the HYMOSTRUC model. In the simulation, attempts are made which deals with multi-components. The stereological aspect, the interaction mechanism, the basic rate equation and the influence factors on the hydration are considered in the model. The numerical experiments are presented. The simulated microstructure is validated and modified according to the experimental results.
In this paper, the influence of the particle size of Superabsorbent Polymers (SAP) for internal curing in High Performance Concrete (HPC) was investigated. Two types of SAP (SAP1 and SAP2) with different sizes were used as curing agents. The autogenous shrinkage of HPC was measured. In addition, the effect of SAP on mechanical properties was also studied. The results reveal that with the same dosage of SAP, the efficiency of internal curing by the SAP with the smaller size (SAP1) is higher than that by the SAP with the larger size (SAP2). By adding SAP into the mixture, the mechanical properties of HPC decrease slightly. By considering the workability, autogenous shrinkage and compressive strength, the SAP with smaller size (SAP1) has better efficiency as an internal curing agent than the other one (SAP2).
In the past few years more and more attention has been devoted to the safety and serviceability as well as durability and sustainability of structures. Meanwhile there are intensive research and development activities going on, e.g. on materials properties, deterioration mechanisms, geometric- and structural design, execution aspect and maintenance. Furthermore, codes and standards on service life design are being discussed and partially established world wide. It is now time to present a focused picture of the current status and future trends in this field, including theory, practice and education. The aim of the symposium is to provide a forum to researchers and practitioners for presenting the newest findings and to discuss new ideas on service life design and serviceability of infrastructural Works, effectiveness of service life design methods and experiences from the practice.
The aim of this thesis was to investigate and to simulate the development of the microstructure, porosity and permeability in hardening cement-based materials. Based on experimental information and the cement hydration model HYMOSTRUC, the microstructural details including porosity, connectivity of pores and pore size distribution were characterized. A network permeability model was built up based on the simulated microstructure and validated with the experiments.
The main purpose of Super Absorbent Polymer (SAP) added into high performance concrete is to prevent or reduce self-desiccation (or autogenous shrinkage) of concrete. The mechanism behind is free water release from saturated SAP lead to an increase of relative humility and to promote further hydration. Compared to plain cement paste, the added SAPs change hydration process and the development of microstructure in concrete. In this contribution, the degree of hydration of cement in cement composites containing SAP are reviewed. The influence of SAP on the development of microstructure properties, i.e. porosity, pore size distribution, morphology and connectivity of bulk cement paste and interface transition zone between cement paste and SPA, the voids introduced by SAP are discussed. It is concluded that the addition of SAP in the mixture increases the hydration degree of cement particle, this leads to a reduction of capillary porosity in the matrix and increase gel pore in the paste. The additional of SAP meanwhile increase the void in the ITZ between SAP and matrix. Micro-computer tomography image shows that the voids introduced by SAP in the mixture are homogenously distributed with an average diameter of 150 µm.
Strain-hardening geopolymer composite (SHGC) lately emerged as a promising alternative to traditional strain-hardening cementitious composite with added advantages of industrial by-product utilization and enhanced sustainability. However, as the design of SHGC requires multi-factor optimization, the application of traditional trial-and-error method is inefficient and hinders the development of this material. This paper aims at the development of a slag/fly ash-based SHGC with low slag content using a micromechanical model to guide the composite mixture design. To this end, experimentally characterized physical properties of fiber, matrix and interface are used as input for the micromechanical model, which serves as a predictive tool for the tensile performance of SHGC. Following the guidance, a slag/fly ash-based SHGC with tensile strain capacity of 4.8% and ultimate tensile strength above 3.8 MPa was systematically developed. The feasibility and effectiveness of using micromechanics as the design basis of SHGC are demonstrated and experimentally verified.
It is commonly understood that the microstructure of cement paste controles the water expulsion from the concrete at high temperature. The pore structure at high temperature has a considerable influence on the spalling behavior. The accumulatieve pore pressure mechanism has become a widely accepted explanation for the explosive spalling in concrete structures. Modeling the physical-chemical changes induced microstructure or micro-cracking evolution of concrete during fire is of great important for engineering practice. In this paper, the influence of the physicochemical change of paste on the microstructure and on explosive spalling is studied qualitatively and quantitatively. In order to examine the consequence of dehydration or decomposition on the various properties of microstructure, a series of experiments were performed, which include thermal analysis, scanning electron microscopy and mercury intrusion porosimetry on different mixes at high temperatures. A numerical model to describe the change of the microstructure of high performance cement paste during heating is proposed. In the model, the consequences of dehydration or decomposition on the various properties of microstructure are modelled. The simulated degradation of materials with heating is validated and calibrated by experiments. The developed model is applied to investigate the influence of some factors such as the degree of hydration, the water/cement ratio and the limestone contents in high performance concrete. This research shows that computational material science is an effective method to provide insights about material behaviour.
