Pore Solution Of Mortar Research Articles

Preparation and properties of cement mortar/ metal hydroxide microcapsules composites

Metal hydroxide microcapsules have been found to possess good sustained-release property, and they could delay the decline of pH values in the pore solution of mortar. In this paper, these metal hydroxide microcapsules were incorporated into cement mortar and It was found that they had no obvious effect on the mechanical properties. In linear sweep voltammetry (LSV) curves, all samples with microcapsules had higher corrosion potential (Ecorr) and corrosion resistance (Rp) values as well as lower corrosion current density (Icorr) values compared with blank sample without microcapsules. These results revealed that the microcapsules had an obvious anticorrosion effect on steel rebars in mortar. EIS tests showed that the anticorrosion effect of metal hydroxide microcapsules was affected by microcapsules dosages and the type of core materials. Compared with the samples with uncoated pure hydroxide, the steel rebar with metal hydroxide microcapsules had higher Ecorr and Rp values, lower Icorr and larger charge transfer resistance values. The corrosion surface on the steel rebars in mortar also confirmed the above conclusion.

Effect of carbonation on the pore solution of mortar

Understanding the changes in the pore solution upon carbonation is crucial with respect to comprehending the mechanisms of reinforcement corrosion in carbonated mortar or concrete.In this paper we used Cold Water Extraction (CWE), a rapid leaching method, on profile ground powder from partially carbonated Portland cement and Portland-fly ash cement mortars to study changes in the pore solution composition.Carbonation decreased the free alkali metal content measured with CWE, which matched with the portlandite profiles determined by thermogravimetry and the carbonation depth detected with pH indicator.The alkali metal uptake by carbonation products was confirmed by SEM-EDS and thermodynamic modelling. Besides the decrease in the alkali metal concentration in the pore solution upon carbonation, we observed for both binders a considerable increase in chlorine and sulphur concentrations. This can further accelerate corrosion in carbonated concrete.

Effect of alkali release by aggregates on alkali-silica reaction

Mortar and concrete specimens were made using one alkali-bearing reactive aggregate, one alkali-free reactive aggregate and one alkali-free non-reactive aggregate in order to determine the effect of an alkali release by an aggregate into the pore solution on the development of ASR using pore water extraction and direct expansion measurements. The fine fraction of the alkali-bearing reactive aggregate was found to be able to release up to 3wt% of its total Na2O content (0.73kgNa2O/m3) into the pore solution of mortar at the age of one year for specimens stored at 60°C. However, there is no evidence that this sodium release influenced the rate of the development of the expansion. Results on mortar specimens also indicated that the amount of Na2O bounded into ASR gel is approximately proportional to the progress of expansion. The same proportionality is however not observed for potassium ion. For concrete specimens, it is clear that Na2O and K2O ions are bound into ASR reaction products, but there is no evidence that the coarse fraction of the alkali-bearing aggregate released alkalis into the pore solution of concrete after one year of testing completed in this study.

Influence of the polysaccharide addition method on the properties of fresh mortars

This study focused on comparison of polysaccharide addition methods, either in powder form, or as a solute in the mixing water. The influence of the methods was assessed by measuring water retention and rheological properties with one cellulose ether and two guar ethers.Polysaccharides were more efficient to enhance water retention and rheological properties when they are pre-dissolved in the mixing water. This is related to differences in polymer concentration in the pore solution of mortar. These differences are not stemming from a difference in dissolution kinetics, but from a difference in adsorption on growing hydrates. Being immediately available when it is pre-dissolved, the admixture slows down the nucleation and growth of hydrates limiting in turn the surface area for further adsorption. Consequently, more molecules are left in the interstitial solution and a lower dosage is required to achieve the overlapping of polymer coils, responsible for the effectiveness of polysaccharides.

Environmental Factor and Concentration of Cl- and OH- in Mortars

The concentration of free hydroxyl ions in pore solutions of mortars is studied, and the effects of hot environment on these ions are reported. The influence of fly‐ash addition is observed and discussed. Fog curing decreases free OH- ions in cement mortar. Fly‐ash mortar retains free OH- ions more satisfactorily. A further decrease in OH- concentration is observed as a consequence of exposure to hot environment. Initially well‐cured fly‐ash/cement mortar performs better in this respect than cement mortar. The ratio of Cl- to OH- in mortars that include Cl- ions increases sharply as a result of hot environment. Fly‐ash inclusion is also beneficial in this situation. Nevertheless a large increase in the Cl-‐to‐OH- ratio is still recorded as a result of hot weather application. The results of this study indicate the importance of applying a suitable curing regime when the concrete contains fly‐ash and/or is exposed to hot weather. The results are relevant to studies concerned with corrosion protection of st...

Effects of a flyash on pore solution composition in calcium and sodium chloride-bearing mortars

The influence of an Australian flyash on Cl − and OH − ion concentration of cement mortar pore solutions was investigated by preparing NaCl and CaCl 2-bearing mortars with 30% replacement of cement with flyash, and analyzing the pore solutions extracted from the mortars cured for prescribed times up to 12 weeks. The flyash had little effect on Cl − ion concentration in pore solutions of mortars below at least the dosage of 2% Cl − as CaCl 2. However, the addition of the flyash considerably reduced Cl − ion concentration in mortars treated with NaCl at 1 and 2% Cl − level. It was also found that the flyash raised the Cl −/OH − ratio in pore solution at the dosages up to 2% Cl − in both calcium and sodium chloride-bearing mortars.