Project progress
Year 2017
Objective: Determining the effect of silica fume, organosilane and water-to-cement ratio on the hydration process, porosity and mechanical strength of cement paste
During the first stage of the project was investigated the effect of silica fume (a), organosilane and water-to-cement ratio on the hydration process (b), porosity (c) and mechanical strength (d) of cement paste. The samples under study were prepared with withe cement in order to reduce the effects of diffusion in internal gradients on nuclear magnetic resonance (NMR) measurements. The samples were prepared with different amounts of silica fume (0-8%) and organosilane (0-2%). They were monitored during the early stage of hydration both using the CPMG technique and the Fast Field Cycling technique. The influence of silica fume and organosilane addition on porosity, pore size and connectivity was further investigated using NMR diffusometry.
The hydration process was monitored at different locations inside the sample using a particular type of instrument, the so called NMR surface explorer. The results showed that the presence of silica fume influences not only the speed of hydration overall, but also sample homogeneity below the surface layer. It was also demonstrated that bleeding does occur even when nano-sized fillers, such as silica fume, are used. There is however a decrease in the quantity of bleed water as compared with the case of simple cement paste, especially when simple colloidal silica nanoparticles are used.
Varying the amount of water in a concrete mix influences its porosity, pore connectivity and the final mechanical properties. That is why, in the present stage of the project NMR techniques were used to reveal pore size distribution and connectivity of cement-based materials prepared at different water-to-cement ratios. A correlation between capillary porosity of the prepared materials and the compressive and flexural strength was established. The investigations rely on using cyclohexane as „spy” molecule thus revealing the whole spectrum of pores inside the hydrated cement pastes. This allowed a qualitative and quantitative analysis of the effects of water-to-cement ratio pore sizes. The cement pastes with higher water-to-cement ratios show an increase in capillary porosity, while the intra-C-S-H and inter-C-S-H pores (also known as gel pores) remain unchanged.
The microscopic investigation based on NMR, SEM and XRay techniques were compared with mechanical strength test performed on the same samples. Thus a correlation between the amount of ingredients, preparation approach, porosity and mechanical strength (flexural, compressive) could be established. These observations will be used in the next stage of the project for the development of new concrete materials with a higher flexural strength.
The hydration process was monitored at different locations inside the sample using a particular type of instrument, the so called NMR surface explorer. The results showed that the presence of silica fume influences not only the speed of hydration overall, but also sample homogeneity below the surface layer. It was also demonstrated that bleeding does occur even when nano-sized fillers, such as silica fume, are used. There is however a decrease in the quantity of bleed water as compared with the case of simple cement paste, especially when simple colloidal silica nanoparticles are used.
Varying the amount of water in a concrete mix influences its porosity, pore connectivity and the final mechanical properties. That is why, in the present stage of the project NMR techniques were used to reveal pore size distribution and connectivity of cement-based materials prepared at different water-to-cement ratios. A correlation between capillary porosity of the prepared materials and the compressive and flexural strength was established. The investigations rely on using cyclohexane as „spy” molecule thus revealing the whole spectrum of pores inside the hydrated cement pastes. This allowed a qualitative and quantitative analysis of the effects of water-to-cement ratio pore sizes. The cement pastes with higher water-to-cement ratios show an increase in capillary porosity, while the intra-C-S-H and inter-C-S-H pores (also known as gel pores) remain unchanged.
The microscopic investigation based on NMR, SEM and XRay techniques were compared with mechanical strength test performed on the same samples. Thus a correlation between the amount of ingredients, preparation approach, porosity and mechanical strength (flexural, compressive) could be established. These observations will be used in the next stage of the project for the development of new concrete materials with a higher flexural strength.
Year 2018
Objective: Determining the influence of silica fume silanization on the hydration process, porosity and mechanical strength of cement paste
During the second stage of the project the influence of silica fume silanization on the hydration stages, porosity development and the mechanical strength was investigated. The silica fume was silanized using the hydrolysis reaction of organosilane followed by its condensation at the surface of silica fume particles. The effects of silanization can be directly observed from SEM images (a) but also are also confirmed by the FT-IR analysis (b) and TDG analysis. NMR relaxation measurements performed on samples containing different amounts of silanized silica fume have revealed a progressive expand of the dormant stage (c) with effects on workability, final mechanical strengths and transportation duration. They have further showed that the presence of silica fume does not influence significantly the pore size distribution. Diffusion measurements performed with the pulse field gradient NMR technique have revealed low connectivity of the porous system, especially for the cyclohexane and ethanol molecules. The lowest connectivity was evidenced in the case of samples containing 6% silica fume, both silanised and non-silanised. The diffusion data agree with the observations from the two dimensional T1-T2 correlation maps (d) . Analysis of the NMR data relative to hydration and pore connectivity, combined with flexural and compressive strength measurements, have allowed us extraction of the best formulation for a concrete material with higher flexural strength and lower permeability.