This research work attempts to reveal the mechanism of alkali corrosion in cement composites in the presence of plasticizers based on polycarboxylates (PCE), naphtha-lene-formaldehydes (SPNF), and ...lignosulfonates by maintaining a high pH of the liquid phase and additionally containing monovalent alkali earth metals in cement stone, as well as stopping this process by introducing an active mineral additive. ASR is studied by changing the relative strain with time according to ASTM C-1260. Deformation changes were confirmed by SEM and RFA studies of hydration products and ASR in the microstructure. Separate use of PCE plasticizers in the cement composition increases deformation by 50% to the 56th day; the use of SPNF increases deformation by 10% compared with the additive-free composition. The use of PLS reduces the relative deformation by 25%. The introduction of silica fume into cementitious composites containing plasticizers actually stops ASR only for a short time. A reduction in deformation during MC use together with plasticizer based on naphthalene sulfonate and polycarboxylate occurs only when the dosage of MS is increased to 20–30%; at a lower dosage, the effect is negative, which also affects the phase composition of the composites. The introduction of MC increases the value of the relative deformation compared with plasticizer compositions based only on PLS. SEM studies have detected microcracks and dense fine-crystalline silicate gel, which cause deformation changes in cement composite samples. Research has shown that concrete modified with SPNF and PCE at the maximum dosage of MC (30%) has minimal deformation rates and can be used to select optimal concrete compositions. The results of this study could help to minimize risks, prevent unacceptable expansion, and ensure the high quality of concrete and concrete products during their use as part of various nature-modifying additives.
This paper analyses the stresses in continuous welded rails on bridges including the aspect of fatigue of rail steel. Furthermore, it examines the possibility to avoid rail expansion joints, while ...simultaneously exploiting the permissible stress capacity of the rail profile 60E1. Accordingly, general application of permissible values of pressure and tensilestresses prescribed in the current European standards was critically analysed. Paper includes specific application aspects of the prescribed stress values for railway bridges in Serbia. General algorithm for reducing the stresses due to the vehicle/track/bridge interaction, which is presented in this paper, was developed by the authors. This algorithm includes all essential parameters of the bridge structure and railway superstructure, as well as the influence of climate conditions and railway route design.
The physical-chemical and heat-physical basis of macro - and microstructures formation, phase content of “cement stone” of low-clinker composite binders for particularly lightweight concrete of ...heat-insulation designation are presented.
The results of corresponding studies on the influence of chemical, mineralogical and phase compositions of the composite binders, their components and formed from them “cement stone” on the activity of the composite binder and its heat-physical characteristics of such cement stone are presented
Submitted work accomplished in the development of the European standard EN 197-1:2000 Cement. Part I. Composition, specification and conformity criteria for common cements.
Silicate hydration is prevalent in natural and technological processes, such as, mineral weathering, glass alteration, zeolite syntheses and cement hydration. Tricalcium silicate (Ca3SiO5), the main ...constituent of Portland cement, is amongst the most reactive silicates in water. Despite its widespread industrial use, the reaction of Ca3SiO5 with water to form calcium-silicate-hydrates (C-S-H) still hosts many open questions. Here, we show that solid-state nuclear magnetic resonance measurements of (29)Si-enriched triclinic Ca3SiO5 enable the quantitative monitoring of the hydration process in terms of transient local molecular composition, extent of silicate hydration and polymerization. This provides insights on the relative influence of surface hydroxylation and hydrate precipitation on the hydration rate. When the rate drops, the amount of hydroxylated Ca3SiO5 decreases, thus demonstrating the partial passivation of the surface during the deceleration stage. Moreover, the relative quantities of monomers, dimers, pentamers and octamers in the C-S-H structure are measured.
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