Portland cement strength development

Ono, Y. Hidaka, T. and Shirasaka, M., "On the Influence of Na O, K O, and MgO on the Development of Strength of Portland Cement Mortar," Reviews, 23rd General Meeting of the Cement Association... 

Soda, Y. Mizukami, K. and Sbirasaka, M., "On the Decline in the Development of the Strength of Portland Cement by the Increase of Magnesia," Reviews, 22nd General Meeting of the Cement Association of Japan, 1968, pp. 48-51. 

Some indication of the respectively contributions of the clinker phases to the strength development of cement is given in Fig. 9. However, these results obtained for individual phases cannot be directly applied to the conditions actually occurring in cement paste, as is apparent also from the heat of hydration values given in Table 10. Fig. 17 schematically shows the sequence of formation of the hydrate phases and the structure development in the setting and hardening of Portland cement. 

The strength of Portland cement concrete may be increased by additional reinforcement. This is usually accomplished by means of steel rods, wires, bars (rebar), or mesh, which are embedded into the fresh and uncured concrete. Thus, the reinforcement renders the hardened structure capable of supporting greater tensile, compressive, and shear stresses. Even if cracks develop in the concrete, considerable reinforcement is maintained. 

Fig. 2.19 Strength development of high-strength flowing concrete containing melamine-based superplasticizer compared to concrete made with 400 kg of normal Portland cement per m in the stiff to low workability ranges (25-100 mm slump). 

Two types of calcium nitrite-based corrosion inhibitors are currently marketed, viz. a set- and strength-accelerating type and a normal-setting type. The former increases the early strength development in concrete. This effect increases with the dosage. Both admixtures are compatible with all types of Portland cements and... 

Alite is the most important constituent of all normal Portland cement clinkers, of which it constitutes 50-70%. It is tricalcium silicate (CajSiOj) modified in composition and crystal structure by incorporation of foreign ions, especially Mg ", AP and Fe. It reacts relatively quickly with water, and in normal Portland cements is the most important of the constituent phases for strength development at ages up to 28 days, it is by far the most important. 

Chemical tests of pozzolanicity have proved of limited use for evaluation, because the 28-day strength depends much more on the w/s ratio than on this property, and there appears to be no effective substitute for direct testing of the relevant properties on mortars or, preferably, on concretes. The degree of pozzolanic activity is, however, important for the development of strength and decrease in permeability at later ages. For equal 28-day strengths, the strengths at 91 days or more normally exceed those of otherwise similar concretes made with pure Portland cements. 

Of the pfa characteristics that influence reactivity, the glass content appears to be much the most important, but specific surface area, glass composition and the effect of stress in the glass caused by the crystalline inclusions may also be relevant (U17). Of external factors, the RH, temperature (C43) and alkali content of the cement are probably the most important. Sulphate ion may also enhance reactivity by promoting the removal of AF from the glass (U17). The rates of the pozzolanic reaction and of strength development are more sensitive to temperature than are those of hydration and strength development for pure Portland cements (e.g. Ref. H52). 

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