Hydration of portland cement

Concrete, Mortar, and Plaster. Citric acid and citrate salts are used as admixtures in concrete, mortar, and plaster formulations to retard setting times and reduce the amount of water requited to make a workable mixture (172—180). The citrate ion slows the hydration of Portland cement and acts as a dispersant, reducing the viscosity of the system (181). At levels below 0.1%, citrates accelerate the setting rate while at 0.2—0.4% the set rate is retarded. High early strength and improved frost resistance have been reported when adding citrate to concrete, mortar, and plaster. 

Fig. 3.14 Schematic diagram of the development of the heat of hydration of Portland cement under isothermal conditions (Bruere). 

ASTM recognizes three types of retarding admixtures type B, which simply retards the hydration of Portland cement type D, which not only provides set retardation but also water reduction and type G, which is a retarding supeplasticizer. The materials that are generally used in these admixtures include ... 

The inherent instability of sulfur-infiltrated concrete in aqueous media illustrated in this study may be the most important factor in utilization, because it will affect long-term durability of the concrete in many natural settings. The Ca(OH)2 produced by the hydration of portland cement is a principal reactant in the leaching process, and while it remains sulfur could be extracted, leaving the matrix vulnerable to other destructive processes. The removal rate of sulfur will vary greatly, depending mostly upon the pH of the immersion medium thus, the concrete deteriorates in alkaline sulfatic soils but is relatively stable in the corrosive neutral sulfatic solutions from the sodium sulfate plant. 

Brucite [magnesium hydroxide Mg(OH)2] is isostructural with CH. It is formed in Portland cement concrete that has been attacked by magnesium salts, and on hydration of Portland cements high in MgO and possibly of Portland cements in general. It has a = 0.3147 nm, c = 0.4769 nm, Z = 1, >, = 2368kgm", oi = 1.561, e = 1.581 (S63). Three polytypes of aluminium hydroxide [Al(OH)3], gibbsite, bayerite and nordstrandite. contain layers essentially similar to those in brucite, but with an ordered pattern of... 

Fig. 7.6 Development of microslruclure during the hydration of Portland cement. Scrivener (S. 9).

The previous treatment on wood-chip made of used timber is necessary, because some wood release harmful extractives which delay the hydration of portland cement. Four kinds of previous treatment were tested, e.g. cold tap water, warm tap water (60 70°C), solutions of 0.1% NaOH and 0.5%NaOH. The strength test results of wood-chip concrete using these treated chip indicated almost the same, because the wood-chip used in this experiment were conifer so the harmful water-soluble extractives were little. After this result, tap water was used as a previous treatment liquid. 

In cements containing pozzolanic additions, the Ume needed to react with pozzolana is provided by the hydration of Portland cement. The hardened cement paste (compared to that obtained with ordinary Portland cement) has a lower lime content and higher content of C-S-H. The amount of pozzolanic addition to Portland cement generally ranges from 20 to 40 % of the total cement content it should be adjusted to the amount of lime produced in the hydration of Portland cement. Any excess of the pozzolanic addition wiU not react and thus will behave as an inert addition. 

The use of polymers must be accompanied by the adoption of a greater mix of energy, so that its effects are more intense and evenly distributed in the cement matrix. The analyze of concrete microstructure is a good way to assess the behavior of mechanical properties and others properties, by the visualization of formed hydrates of Portland cement and its distribution. Research into the combination of polymers with different characteristics appears to be a noteworthy path to continue. 

Evaluation of the Hydration of Portland Cement Modified with Polyvinyl... 

T. Knudsen, Modeling hydration of Portland cement — the effect of particle size distribution, in ... 

Z. Su, J.M. Bijen, J.A. Larbi Influence of polymer modification on the hydration of portland cement. Cement Concrete Research 21/1991, pp. 535-544. 

The water content can vary producing different hydrate phases. If sulfur is present (in gypsum) the reaction becomes more complex and leads to the formation of the mineral ettringite, Ca6Al2(S04)3(0H)i2-26H2O, during the hydration of Portland cement. 

In the first decade of infrared research on the study of Portland cements, Vazquez (1%9), was a lead the way in the study by infrared spectroscopy the main present compounds in the Portland cement but also later, made some research about the carbonation processes of calcium aluminate cements. Also, the hydration of Portland cement and its constituents was... 

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