Interaction of water with supplementary cementitious materials: Hydration mechanism, microstructure and moisture transport
Doctoral thesis, 2023
Results show that the dissolution theory fails to explain anomalous hydration of tricalcium silicate at high water to solid ratio. A new hypothesis in this study proposes that calcium silicate hydrate (C-S-H) primarily nucleates within the near-surface region, and this hypothesis bridges the gap between dissolution and protective layer theories. The designed device performs well in monitoring water interaction with SCMs. The evolution of electrical conductivity in hydrating pastes closely relates to chemical reaction processes and can be classified into four stages. The growth rate of the formation factor indicates the reactivity of different binders. Blending SCMs refines the pore structure, decreases pore connectivity and results in a higher formation factor. SCMs affect the pore structure of, the phase assemblage and water dynamics. The mesoscale pore structure in pastes with SCMs can be well indicated by water vapour desorption isotherms, but ion effects on water vapour equilibrium pressure must be considered when calculating pore size distribution. A novel approach works well in evaluating the hydration degree of SCMs by use of water vapour sorption and thermodynamic modelling. Thermoporometry and broadband dielectric spectroscopy effectively characterise moisture distribution and dynamics in hcps, respectively. SCMs have limited effects on the dynamics of structural water, primarily influencing water dynamic in small gel pores and interfacial polarization. The first drying process decreases the volume of unfrozen water (< ~2.4 nm) under various levels of relative humidity. Gel pores coarsen significantly during the drying between 75 % and 50 %.
Change of microstructure alters the transport of moisture and chloride in hcp. The decrease in both moisture transport coefficient and chloride migration coefficient induced by SCMs is notably more significant in hcp with a higher water to binder ratio. The modified moisture transport in blended systems is primarily due to pore structure refinement, specifically the reduction in pore connectivity. Both the formation factor and porosity of small pores determine the moisture transport properties of hcp, with the formation factor being more significant at high RH and the porosity of small pores being more significant at low RH. The effect of SCMs on chloride is also due to the decrease in pore. A simplified model based on the formation factor of hcp can be used to estimate the chloride migration coefficient for the blended pastes and mortars.
The upgraded device provides a reliable non-destructive monitoring of concrete performance. Formation factor and ultrasonic pulse velocity are reliable indices for concrete strength; however, formation factor exhibits the optimal performance. This study provides insights into the mechanism of how water interacts with cementitious materials and a new non-destructive monitoring method to promote the application of SCMs in sustainable concretes.
Supplementary cementitious materials
Chalmers, Architecture and Civil Engineering, Building Technology
New insights into the reaction of tricalcium silicate (C<inf>3</inf>S) with solutions to the end of the induction period
Cement and Concrete Research,; Vol. 152(2022)
Real-time monitoring the electrical properties of pastes to map the hydration induced microstructure change in cement-based materials
Cement and Concrete Composites,; Vol. 132(2022)
Moisture and ion transport properties in blended pastes and their relation to the refined pore structure
Cement and Concrete Research,; Vol. 161(2022)
Using water vapour and N2 isotherms to unveil effects of SCMs on nanopores and evaluate hydration degree
Cement and Concrete Research,; Vol. 164(2023)
Long-term performance of reinforced concrete under a de-icing road environment
Cement and Concrete Research,; Vol. 164(2023)
L. Huang, H. Jansson, J. Swenson, L. Tang, Z. Yang, Distribution and dynamics of water in the blended pastes unraveled by thermoporometry and dielectric properties
L. Huang, L. Tang, I. Löfgren, N. Olsson, A. Ahmadi, O. Esping, Y. Li, Z. Yang, Non-destructive test system to monitor hydration and strength development of low CO2 concrete
Examples of SCMs include fly ash, slag and limestone powder. Some of them are industrial by-products that would otherwise be disposed of in landfills, but instead can be used to create stronger and more durable concrete. Although benefits of using SCMs in concrete extend beyond just reducing the carbon footprint, the use of diverse SCMs induce difficulties in controlling and predicting the performance of concrete. When using traditional methods to predict the right time for laying or finishing concrete containing SCMs, the inaccurate predictions will result in humidity-related issues such as cracking and mould growth, causing a threat to human health and safety. Therefore, a comprehensive understanding of the properties of the blended concrete is needed to establish appropriate models for better control the performance.
This dissertation has conducted an in-depth study on exploring the impact of SCMs and related additives on hydration of cementitious materials and microstructure change, and their relationship to transport processes. A device was designed to continuously monitor the effect of SCMs on hydration-induced structure change, and it was subsequently upgraded to monitor the hardening process of concrete containing SCMs. The work in this dissertation contributes to promote the high-quality use of SCMs in sustainable concretes.
Water in "Green" Cementitious Materials
Cementa (173015), 2020-11-02 -- 2022-04-30.
Formas (2018-01430), 2019-01-02 -- 2022-04-30.
Development Fund of the Swedish Construction Industry (SBUF), 2019-01-01 -- 2022-04-30.
Thomas Concrete Group, 2019-01-01 -- 2022-04-30.
Other Materials Engineering
Areas of Advance
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5337
via Zoom online meeting and physically in Jiading campus of Tongji University, Shanghai.
Opponent: Prof. Kefei Li, Tsinghua University, China