Department of Mechanics: Seminar: Abstract Ibarra 2016

Luis Baquerizo Ibarra

Cement hydrates and their chemically bound water content are sensitive to changes in relative humidity (RH) and temperature. Up to 15 different cement hydrates can be found in hardened concrete, and the final phase constitution depends on the type of cement and the mineral component used. This may cause specific solid volume changes affecting dimensional properties of hydrated cement paste such as shrinkage, swelling and expansion, and therefore impact the performance and the transport properties of cementitious materials. The present talk studies the impact of drying conditions on the structure and thermodynamic properties of crystalline cement hydrates in different hydration states (i.e. varying molar water contents).The cement hydrates studied include the most important AFm and AFt phases present in different types of cements.

A novel multi method approach, including XRD, TGA, DSC, sorption balance measurements, sorption calorimetry and the hydrate pair / humidity buffer method, was used to derive physico-chemical boundary conditions and the thermodynamic properties of the studied hydrated phases. The stability and hydration states of AFm phases depend on the anion content and the exposure conditions. Some phases such as monosulfoaluminate and hydroxy-AFm are very sensitive to different relative humidities. On the other hand monocarboaluminate and strätlingite present very good volume stability with varying RH. Ettringite shows a strong hysteresis during desorption/adsorption, and the thermodynamic properties associated with its decomposition and reformation were determined.

The experimental results were included into a thermodynamic model capable of predicting the response of cementitious systems considering the true crystal water content on the final phase assemblage in two different scenarios: i) during hydration, even at conditions where the amount of water added was insufficient for complete hydration, and ii) during drying and re-wetting processes in already hydrated systems. Our work hence opens the possibility to model the response of various cement materials exposed to different climatic conditions and to engineer cementitious systems with respect to minimizing volume changes in the course of drying, which may positively impact properties like drying shrinkage and total porosity.

Brief bio

Luis Baquerizo Ibarra is a cement technologist in LafargeHolcim, Ltd. He improves and develops new cement solutions, focuses on performance in applications and provides support the development and implementation of advanced testing procedures for performance assessment of cementitious products. He holds bachelor in Mechanical Engineering, a Master in Materials Science and a Ph.D. in Cement and Concrete Science. He has worked/studied in 4 different countries during the past 7 years. He deals particularly with:

• Optimization of mass concrete structures.
• Early age properties of concrete.
• Analysis of supplementary cementitious materials (SCM's): slag, fly ash, natural pozzolans, metakaolin, silica fume.
• Synthesis of clinker phases.
• Hydration analysis of cement blended with different SCM's using XRD-Rietveld analysis and thermal analysis.
• Thermodynamic modelling of cement hydration and drying.