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• The early properties of cement pastes modified by anionic, cationic and nonionic PAM were contrastively studied. • The absorption and hydration of cement pastes with different ionic PAMs were investigated. Polyacrylamide (PAM) has been widely applied as a viscosity modifier to optimize the workability of cement-based materials, but PAMs with different ionic types may show various effects, which is often ignored in practical engineering. In this paper, the early properties including the rheology, flowability, and setting of cement pastes modified by three ionic PAMs (anionic APAM, cationic CPAM, and nonionic NPAM) were contrastively studied. The absorption and hydration of cement pastes with different ionic PAMs were further investigated. Moreover, the contributions of physical flocculation and chemical hydration on the structural build-up of cement pastes were quantified by combining the static yield stress and heat release at the same time scale. The results indicated that three ionic PAMs showed different effects on the structural build-up, fluidity and setting of fresh cement pastes, which were dominated by the different physical flocculation and hydration retardation effects of three ionic PAMs on the cement pastes. The order of flocculation and hydration retardation effects of these three ionic PAMs was APAM ≫ NPAM > CPAM, which was concentration-dependence and evolved over times. The reason is mainly due to the distinct molecular structures and physicochemical properties of three ionic PAMs and their different adsorption behaviors with cements particles. [ABSTRACT FROM AUTHOR]

• Time-dependent rheological behavior after continuously shearing was investigated. • A parameter describing the disappearance of shear thinning at down curve was proposed. • Physical and chemical properties affect the evolutions of rheological properties with shearing. Shear history exerts a great impact on the rheological properties, and thus the consolidation and construction quality of concrete. This study experimentally investigated the time-dependent rheological behavior of cementitious pastes under continuously shear mixing. A parameter describing the disappearance of shear thinning at the decelerating curve was proposed. Results indicate that continuous shear mixing could not effectively hinder the development and evolution of thixotropy and yield stress of cementitious pastes over time. After continuously shear mixing for a while, the critical shear rate corresponding to the disappearance of shear thinning increased. Cementitious pastes tended to exhibit shear thinning behavior at relatively lower shear rate ranges. At higher shear rates, the rheological behavior of cementitious pastes after continuously shearing was strongly dependent on the composition of cementitious materials. The evolutions of rheological properties after continuously shearing were associated with the physical nature and chemical hydration of cementitious pastes. [ABSTRACT FROM AUTHOR]

• The rheological properties of AAS pastes have been improved by low surface free energy mineral admixtures. • The surface free energy properties of low surface free energy mineral admixtures have been determined by IGC method. • The interparticle forces were calculated to reveal the mechanism for rheological improvement. This study investigates the effect of low surface free energy mineral admixtures (CaF 2 -dominated fluorite (FL) and fluorine-containing lithium slag (LS)) on the rheological behavior of alkali-activated slag (AAS) pastes. The fluidity, rheological behavior, surface charge properties and surface free energy properties were tested. The interparticle forces based on extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory were calculated to understand the mechanism for the rheological behavior improvement. The results revealed that both FL and LS could improve the fluidity and decrease the yield stress and plastic viscosity of AAS pastes. Furthermore, the attraction is manifested by the sum of electrostatic, van der Waals, and Lewis acid-base forces, and this value decreases with increasing LF or LS content, implying that the particle dispersion in AAS pastes is improved. Furthermore, observing flocculent structures captured by the metallographic microscope proves the better dispersion of AAS pastes after adding FL and LS. Moreover, incorporating LS or FL decreases the flexural and compressive strengths of AAS mortars. [ABSTRACT FROM AUTHOR]

For lightweight chemical foaming mixtures, it is a technical challenge to control the stability while reducing its density. In this study, cenospheres (CP, a lightweight component) was used to replace part of fly ash (FA) to prepare ultra-lightweight foamed geopolymer concrete (UFGC), and the relationship between the fresh properties of the paste and the stability of UFGC mixture were discussed. Results show that incorporating CP to the slag-FA system can effectively reduce the reaction rate and heat release of the geopolymer paste, thereby effectively slowing down the decomposition rate of H 2 O 2. Different from prefabricated foams, the initial size of the foams decomposed by H 2 O 2 is also affected by the fresh properties of the paste. Meanwhile, the float of bubble and the drainage of the paste are controlled by the yield stress of the paste in the stable stage. As the CP substitution ratio increases, the initial yield stress of the paste decreases, which is beneficial to generate smaller initial bubbles. However, for bubbles of the same size, the low yield stress of the paste is detrimental to its long-term stability. Finally, the UFGC mixture with 50% CP has better stability and the best hardened pore structure. In addition, the calculated critical yield stress that prevents the foamed mixture from collapsing is compared with the initial yield stress of the geopolymer paste. [ABSTRACT FROM AUTHOR]