Many calorimetric studies have been carried out to investigate the reaction process of alkali-activated slag paste. However, the origin of the induction period and action mechanism of soluble Si in the dissolution of slag are still not clear. Moreover, the mechanisms behind different reaction periods are not well described. In this study, the reaction kinetics of alkali-activated slag paste was monitored by isothermal calorimetry and the effect of soluble Si was investigated through a dissolution test. The results showed that occurrence of the induction period in hydration of alkali-activated slag paste depended on the presence of soluble Si in alkaline activator and the soluble Si slowed down the dissolution of slag. A dissolution theory-based mechanism was introduced and applied to the dissolution of slag, showing good interpretation of the action mechanism of soluble Si. With this dissolution theory-based mechanism, origin of the induction period in hydration of alkali-activated slag was explicitly interpreted.
This study investigates the drying shrinkage and the shrinkage-induced stress of alkali-activated blast furnace slag and fly ash concrete (AC) in comparison with ordinary Portland cement concrete (OC). For samples that were dried from 1 day after casting, the drying shrinkage of AC was much higher than that of OC. For samples that were stored in a sealed condition for 28 days before drying, the subsequent drying shrinkage amplitudes of AC and OC were comparable. In both conditions, the stresses generated in AC were higher than in OC at the beginning, but experienced great reductions after certain ages, reaching less than one-fourth of the stresses in OC in the end. The stresses decrease, i.e. relaxation in AC was attributed to the pronounced non-elastic deformability of CASH gels. The non-elastic deformability of AC reduced the risk of thorough cracking, but maybe at the expense of the development of local microcracks. It is recommended to protect AC from drying at an early age to avoid micro and macrocracking.
Water molecules exist as two spin isomers, differing by the relative orientation of the nuclear spins of the two hydrogen atoms: either antiparallel (para-water, S=0) or parallel (ortho-water, S=1) [1]. The transition between these nuclear spin states can be achieved through magnetic symmetry breaking via a field gradient across the spins applied by a suitably placed magnetic moment for a sufficiently long time [2]. The contradictory mechanisms of interaction between water or an aqueous solution and magnetic field were reviewed, especially the one expanded on Dynamically Ordered Liquid Like Oxyanion Polymers (DOLLOP) [3]. Then the state of art agreements that have been proved by reproductive experiments or theories were discussed. A new hypothesis for the magnetic effects on the interconversion of nuclear spin isomers of water at the interface of water-O2 was proposed, as well as its applicability in the structure modification of C-S-H.
Excessive F- in drinking water due to natural and anthropogenic activities is a serious health hazard affecting humans worldwide. In this study, a comparative assessment was made of eight mineral-based materials with advantageous structural properties for F- uptake: layered-double-hydroxides (LDHs), geopolymers, softening pellets and struvite. These materials are considered low-cost, for being either a waste or by-product, or can be locally-sourced. It can be concluded that Ca-based materials showed the strongest affinity for F- (Ca-Al-CO3 LDHs, slag-based geopolymer, softening pellets). The Langmuir adsorption capacity of Ca-Al-CO3 LDHs, slag-based geopolymer and softening pellets was observed to be 20.83, 5.23 and 1.20 mg/g, respectively. The main mechanism of F- uptake on Ca-Al-CO3 LDHs, Mg-Al-Cl LDHs, slag-based geopolymers and softening pellets was found to be sorption at low initial F- concentrations (<10 mg/L) whereas precipitation as CaF2 is proposed to play a major role at higher initial F- concentrations (>20 mg/L). Although the softening pellets had the highest Ca-content (96-97%; XRF), their dense structure and consequent low BET surface area (2-3 m2/g), resulted in poorer performance than the Ca-based LDHs and slag-based geopolymers. Nevertheless, geopolymers, as well as struvite, were not considered to be of interest for application in water treatment, as they would need modification due to their poor stability and/or F- leaching.
The aim of this paper is to present the failure process of cement paste at different ages subjected to tensile loading. The input structure (cement paste) is generated by means of the cement hydration model HYMOSTRUC3D. A 2D-slice of this generated microstructure is subsequently transferred to the Delft Lattice Model, in which the failure process is analysed. Failure of cement paste microstructures at different degree of hydration, various water-cement ratios and different particle size distributions are analysed and discussed in the paper.
Known as the “concrete cancer”, alkali-silica reaction (ASR) has attracted academie and industrial interests since its first report in the 1940s. The mechanism of ASR governing the reaction process and the consequent deterioration of concrete structure is one of the most popular research topics due to its scientific and industrial signiftcance. Due to the heterogeneousness of concrete, however, it is extremely difficult to explore the fundamental mechanism and eventually, conclude a reliable and practical guidance for the mitigation of ASR by studying an in situ concrete. In consideration of limiting the heterogeneousness of concrete, therefore, a Chemical model system can be used for simulating the physico-chemical interactions between the reactive silica present in aggregates and various constituents of cement paste. In this work, the necessity of creating a Chemical model system to simulate alkali-silica reaction under laboratory conditions from a Chemical point of view is given. Many Chemical model systems ifom the previous studies are reviewed. Critical factors which need to be considered during the creation of the model system are discussed to provide practical suggestions.
In this paper, we concluded methods, characteristics and key issues of electroless Co plating from non-aqueous at room-temperature; and discussed the effected factors of technical condition and the main research progress at time, and we also prospected the improvement of this way.
The equivalent conductivities of the two main silicate species, [[EQUATION]] and [[EQUATION]], are indispensable parameters to study many physico-chemical phenomenons of silicate materials in electrolyte solutions (e.g., diffusion, adsorption, or phase transformations). However, literature data exhibits inconsistency and has received only limited scholarly attention. In this paper, a conductivity model for mixed electrolytes is established and verified. With this model the equivalent conductivities of the two silicate species were measured with electrochemical impedance spectroscopy (EIS) in the temperature range of 4.7 to 35.3 °C. The accuracy of the results is fully discussed via multiple perspectives. This work lays the foundation for quantitative investigation of phase transformation of silicate materials with potentiometric method.
