Towards more sustainable construction–application of superabsorbent polymers in cementitious matrices with reduced carbon footprint

Construction industry is constantly searching for sustainable innovations to mitigate negative environmental impacts. Ground granulated blast-furnace slag (GGBS) is a well-known supplementary cementitious material which contributes to reduction of energy and CO2 emissions from cement industry. However, its use in cementitious systems leads to materials with high cracking susceptibility due to their greater autogenous shrinkage triggered by self-desiccation processes. This problem is even more pronounced when concrete is exposed to severe dry-hot weather conditions, such as in North Africa. In order to mitigate this negative effect of cracking, internal curing agents in the form of Superabsorbent polymers (SAP) can be successfully used. This approach leads to more durable cement based materials and in turn more sustainable constructions

Mechanism of microstructural modification of the interfacial transition zone by using blended materials

Applying blended materials with finer particle size or high reactivity could be an effective and economic way for improving the microsturcture of interfacial transition zone (ITZ). In this study, the porosity characteristics of ITZ in concrete made with OPC and blended binders were determined quantitatively by using backscattered electron microscopy (BSE) image analysis and mercury intrusion porosimetry (MIP) measurements. This paper especially focused on the effects of slag and limestone filler on the thickness and pore structure of the ITZ. Results indicated that the porosity at each distance reduces with increasing limestone filler from 0 to 5%, and a significant increase is observed in the sample with 10% of limestone filler. The addition of 5% of limestone filler is able to densify the pore structure of both ITZ and bulk matrix. The reduction in pore volume in the range coarser than 100 nm contributed to the largest decrease in the total pores. Increasing the incorporation level of limestone filler to 10% resulted in an increase in the total porosity. The influences of slag on the porosity characteristics were highly dependent on the replacement level and the determined pore size regions. The addition of 35% of slag reduces the porosity at all distances and produces a denser microstructure both in the ITZ and bulk cement matrix. However, this improvement disappears when the substitution amount reaches to 70%. The incorporation of slag as a partial substitute for Portland cement tends to refine the pore structure

Permeability of Concrete with Recycled Concrete Aggregate and Pozzolanic Materials under Stress.

The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the permeability of RAC is much lower than that of the reference concrete due to the on-going hydration and the pozzolanic reaction provided by the PHS and GGBS additives in the RAC mixture. The permeability of chloride under flexural load is much more sensitive than that under compressive load due to the differences in porosity and cracking pattern. At low compressive stress levels, the permeability of chloride decreased by the closing of pores and microcracks within RAC specimens. However, in a relatively short time the chloride diffusion coefficient and the chloride content increased rapidly with the increase of compressive stress when it exceeded a threshold stress level of approximate 35% of the ultimate compressive strength. Under flexural stress, the chloride transport capability increased with the increase of stress level and time. At high compressive and flexural stress levels, creep had a significant effect on the permeability of chloride in the RAC specimens due to the damage from the nucleation and propagation of microcracks over time. It is apparent that mortar cracking has more of a significant effect on the chloride transport in concrete than cracking in the interfacial transition zone (ITZ)

Nutrient retention of vegetated buffer strips on a cropped field and a pasture

The effects of 10-meter wide grass buffer strips (GBS) and vegetated buffer strips under natural vegetation (VBS) on losses of sediment, phosohorus and nitrogen from cropped soil plots has been studied for 15 years on Lintupaju field at Jokioinen. The results have been compared with those from 70-m-long and 18-m-wide plots without buffers