Alkali Tolerance of Concrete Internal Curing Agent Based on Sodium Carboxymethyl Starch

Internal curing agents (ICA) based on super absorbent polymer have poor alkali tolerance and reduce the early strength of concrete.An alkali tolerate internal curing agent (CAA-ICA) was designed and prepared by using sodium carboxymethyl starch (CMS) with high hydrophilicity,acrylic acid (AA) containing anionic carboxylic group and acrylamide (AM) containing non-ionic amide group as the main raw materials.The results show that the ratio of CAA-ICA alkali absorption solution is higher than that existing ICA,which solves the low water absorption ratio of the ICA in alkali environment.The water absorption ratio of CAA-ICA in saturated Ca(OH)_(2) solution is 95.8 g·g^(-1),and the alkali tolerance coefficient is 3.4.The application of CAA-ICA in cement-based materials can increase the internal relative humidity and miniaturize the pore structure.The compressive strength of mortar increases up to 12.95%at 28 d,which provids a solution to overcome the reduction of the early strength.

Comprehensive evaluation of tolerance to alkali stress by 17 genotypes of apple rootstocks

Alkaline soils have a great inlfuence on apple production in Northern China. Therefore, comprehensive evaluations of toler-ance to such stress are important when selecting the most suitable apple rootstocks. We used hydroponics culturing to test 17 genotypes of apple rootstocks after treatment with 1：1Na2CO3and NaHCO3. When compared with the normaly grown controls, stressed plants produced fewer new leaves, and had shorter roots and shoots and lower fresh and dry weights after 15 d of exposure to alkaline conditions. Their root/shoot ratios were also reduced, indicating that the roots had been severely damaged. For al stressed rootstocks, electrolyte leakage （EL） and the concentration of malondialdehyde （MDA） increased while levels of chlorophyl decreased. Changes in root activity （up or down）, as wel as the activities of peroxidase （POD）, superoxide dismutase （SOD）, and catalase （CAT） were rootstock-dependent, possibly relfecting their differences in alkali tolerance. Using alkali injury index （AI）, adversity resistance coefifcients （ARC）,cluster analysis, and evaluation of their physiological responses, we classiifed these 17 genotypes into three groups： （1） high tolerance： Hubeihaitang, Wushanbianyehaitang, Laoshanhaitang Ls2, Xiaojinbianyehaitang, and Fupingqiuzi; （2） moderate tolerance： Pingyitiancha, Laoshanhaitang Ls3, Hubeihaitang A1, Deqinhaitang, Balenghaitang, Maoshandingzi, Shandingzi, and Xinjiangyepingguo; or （3） low tolerance： Pingdinghaitang, Hongsanyehaitang, Xiaojinhaitang, and Sanyehaitang. These results wil signiifcantly contribute to the selection of the most suitable materials for rootstocks with desired levels of tolerance to alkali stress.