Functionality of mortar and concrete mixes is regulated by surfactants, which act as plasticizers. The molecular structure of these admixtures can be changed during hydration of alkali-activated cements (AAC). The objective was to determine the chemical nature of plasticizers effective for property modification of mortars and concretes based on AACs with changing content of granulated blast furnace slag from 0 to 100 %. The admixtures without ester links become more effective than polyesters when content of alkaline component increase. The admixtures effective in high alkaline medium were used in dry mixes for anchoring (consistency of mortar 150 mm by Vicat cone; 1 d tensile strength in bending / compressive strength of mortar 6.6 /30.6 MPa) and in ready-mixed concretes (consistency class changed from S1 to S3, S4 with consistency safety during 60 min; 3 d compressive strength of modified concrete was not less than the reference one without admixtures).
Проаналізовано проблему пластифікації цементів, лужне середовище яких визначає при-сутність сполук лужних металів, та запропоно-вано шляхи її вирішення. В якості альтернативи суперпластифікаторам на основі складних поліе-фірів запропоновано широке коло поверхнево-ак-тивних речовин, придатних для пластифікації лужних цементів. Органічні сполуки системати-зовані за ефективністю дії як пластифікатори лужних цементів Ключові слова: лужний цемент, хімічна добав-ка, поверхнево-активна речовина, гранульований доменний шлак, цементне тісто, пластична міц-ність Проанализирована проблема пластификации цементов, щелочную среду которых определя-ет присутствие соединений щелочных метал-лов, и предложены пути ее решения. В каче-стве альтернативы суперпластификаторам на основе сложных полиэфиров предложен широ-кий круг поверхностно-активных веществ, при-годных для пластификации щелочных цементов. Органические соединения систематизированы по эффективности действия в качестве пластифи-каторов щелочных цементов Ключевые слова: щелочной цемент, химиче-ская добавка, поверхностно-активное вещество, гранулированный доменный шлак, цементное тесто, пластическая прочность UDC 691.5
Nowadays, alkali-activated cements (AACs) are the most promising alternatives to ordinary portland cement (OPC). Such cements characterized by better strength and corrosion resistance that determine improved durability of materials based on them. However, the shrinkage of AAC systems is noticeably higher compared with OPC. The purpose of this work was to study the shrinkage behavior of alkali-activated slag cement (AASC) pastes. To improve early age performance of AASCs – OPC and Ca(OH)2, as mineral additives, were added to the designed cement mixtures. The properties, like, flexural and compressive strength of cement mortars, chemical shrinkage, autogenous shrinkage and drying shrinkage of cement pastes were studied. The results showed that the chemical shrinkage, autogenous shrinkage and drying shrinkage at 28 days were between 0.064 – 0.074 ml/g, 4.5 – 7.9 mm/m and 3.3 – 4.9 mm/m, respectively. The relationship between the nature of alkaline components, the type of mineral additives and the shrinkage behavior of cements were discussed.
A thermodynamic analysis of the reactions of calcium chloride and calcium nitrate with tricalcium aluminate when used as a hardening accelerator for portland cement, as well as decomposition reactions of calcium hydrochloraluminate (CHChA) and calcium hydronitroalyuminate (CHNA) formed during the hardening was performed. The conditions of stable existence of CHChA and CHNA in the cement matrix were established.
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