چكيده به لاتين
The research aims to examine the physical effects of internal components of self-compacting concrete mixture on rheological properties and thixotropy. This includes analyzing the packing density and the paste film and mortar film thickness. Additionally, the study seeks to investigate the rheological properties and thixotropy of self-compacting concrete containing tuff as a cement substitute admixture, comparing it with silica fume.
The research is divided into two main parts. The first part investigates the effect of internal components of self-compacting concrete on its properties in both fresh and hardened states. This involved creating mixtures in three groups with different variables. The first group consisted of self-compacting concrete mixtures with varying aggregate distribution (0.2, 0.25, 0.3, and 0.35 in the Fuller-Thomson relationship). The second group included mixtures with tuff powder and silica fume as 8% and 15% replacements for cement, respectively. The third group comprised mixtures with varying amounts of cement (±5%) compared to the reference mixture, while maintaining the same amount of water. The tests conducted to evaluate the properties of the mixtures in fresh state, included workability, rheology, thixotropy, wet packing density, setting time, and compressive strength and Ultrasonic Pulse Velocity (UPV) tests to assess the mechanical properties and internal structure of hardened concrete.
In the second part of this research, we discussed the relationship between workability and rheology test results, packing density and rheology properties, setting time and thixotropy. We also investigated the effect of paste film and mortar film thickness on yield stress, plastic viscosity and thixotropy. The results indicate an optimal amount of sand and coarse aggregate for the self-compacting concrete mix, resulting in the lowest rheological properties (the concept of optimal particle size distribution of aggregate) The packing density results also showed that the mixture has higher density at this optimum value. These conditions occur when the aggregate distribution is done with a modulus of 0.3.
Additionally, using 15% tuff as a partial substitution of cement increased yield stress and plastic viscosity by 100% and 14%, respectively, and decreased thixotropy by 12% compared to the reference mixture. However, the tuff-containing mixture had a 2% lower packing density than the reference mixture.
Finally, by comparing the results, it was found that increasing the paste film thickness decreases the plastic viscosity of the mixture, while increasing the mortar film thickness increases plastic viscosity. Also, thixotropy increases with paste film thickness and decreases with mortar film thickness. On the other hand, there was no clear relationship between the paste film thickness and mortar film thickness with the yield stress.
