Intra granular porosity of mineral powders: modeling and experimentation

Abstract

Recycled concrete aggregate (RCA) possess high water absorption, due to the porosity of the attached hardened cement paste they contain. Fine particles of RCA are composed of larger amounts of hardened cement paste, which makes their valorization even more difficult in concrete or mortar. One way to valorize these fine particles could be to use them as mineral addition, however their water absorption coefficient has to be determined, which is tricky for powders. The objective of this work is to estimate the remaining intra granular porosity of a ground powder using two different original approaches. The first modelling approach considers that the porous monolith material is composed of series of pores with characteristic volumes. A pore is considered opened due to grinding if it is cut by the surface of the particle and if its size is larger than the smallest inter granular pore. The remaining porosity after grinding is computed from the pore size distribution of the monolith material and the particle size distribution of the powder. The second experimental approach is based on mercury intrusion porosimetry tests performed on the powder. The separation between inter and intra granular porosity allows the estimation of the powder's remaining porosity. The obtained results show a good agreement between the two approaches in the case of disconnected pores. However, in the case of connected porosity, the experimental approach over estimates the amount of inter-granular porosity.

Substitution of limestone filler by waste brick powder in self-compacting mortars: Properties and durability

“…Previous investigations realized on this material [35] showed that the porosity of WBP was very low after grinding the brick particle. Preliminary tests showed however that the substitution of limestone filler by WBP had a negative impact on the workability: preventive measures (superplasticizers or extra water addition) are required to control the workability of J o u r n a l P r e -p r o o f mixture.…”

“…The potential to use waste ceramic powder in SCC as cement replacement up to 15% is suitable due to the positive effects on the fresh state properties on SCC. Bouarroudj et al [35] estimated the remaining intra granular porosity of a ground powder using modelling approach and experimental approach with the help of mercury intrusion porosimetry. The results showed that porosity of the ground brick is almost eliminated by the grinding procedure (2% and 2.1% with the modelling approach and experimental approach).…”

Use of grinded hardened cement pastes as mineral addition for mortars

“…-The remaining intra granular porosity (φ ) of the powder has been computed with the theoretical model developed by Bouarroudj et al [23,24]. This model is presented with (eq.2) where R j corresponds to the radius of grain, r i is the pore radius, is the initial porosity, x i is the volume fraction of each size of pore, y j corresponds to the volume fraction of each size of grain, and R 5% coresponds to the radius of 5% of the passing particles.…”

“…Zhao et al [17] and Le et al [18] showed that standard EN 1097-6 [19] or IFSTTAR protocol [20] to measure the WA can only be used for particles larger than 0.5mm, due to agglomeration effects between the finer particles [21,22]. Up to know only Bouarroudj et al [23,24] proposed a method to estimate the WA of finer particles (< 500µm) based on a theoretical approach. This method takes into account the particle size distribution of the powder and the pore size distribution of the monolith (the coarse material before grinding into a powder) by mercury intrusion porosimetry.…”

Effects of Crushing and Grinding on the Porosity of Hardened Cement Paste

“…This method is based on the linear relationship between the WA and cement paste content, where the WA is obtained by interpolation. Another method, based on a theoretical model, has been proposed by [21]. This model is based on the particle size distribution of the ground material and the pore size distribution obtained from the monolith using MIP.…”