The Effects of Cellulose Ethers and Limestone Fillers in Portland Cement-Based Mortars by 1H NMR relaxometry

Resumo

The effect of cellulose ethers (CE) and limestone filler added in nowadays receipts to improve some thermal and hygroscopic properties of construction materials based on plaster mortar were evaluated by ¹H 1D nuclear magnetic resonance (NMR) T₂-distributions, distribution of pore size distribution, scanning electron microscopy images and compressive testing. The CE polymer is used in three concentrations of 0.5, 1.0 and 2.0 % from cement mass, and the limestone filler was used into a fixed concentration of 10 % from cement mass. The ¹H 1D NMR Carr-Purcell-Meiboom-Gill decays measured for all samples were analyzed by inverse Laplace transform leading to a series of T₂-distributions generally characterized by four peaks associated, from low to high T₂-values, with bound water to cement components, and then with small, medium and large pores. A series of measurements were performed at 28 days after sample preparation, and then the samples were stored for 2 months in water in order for the pores to be saturated and measured again. From the ¹H 1D NMR T₂-distributions, into a spherical pores approximation, the distributions of pores sizes were calculated and characterized. For all samples a series of SEM images were recorded with different magnitudes and which, in particular were used to estimate the surface relaxivity factor used in the determination of pores distributions. We estimate the effect of CE polymer and limestone filler on the compression rate which was also correlated with the bound water percentage.