Strength Portland cements

High-early-strength portland cement as specified in JIS R 5210 (Portland Cement) was used in all the mortar mixes for artificial woods. 

Two types of pulp sand mortar were used as the core plate of sandwich specimens. Mortar of Type M was made by mixing high-early-strength Portland cement, silica fume and pulp sand. Mortar of Type P was made directly with pulp sand. Mix proportions of each type of mortar are shown in Table 1 and Table 2. Pressurized forming was used to produce mortar plates of each type, whose pressure was lOMPa. Then specimens were put in a moist room of 20 C for about one day. After steam curing at 50 C for 24 hours, they were autoclave-cured on condition of 180 C for 3 hours. Finally they were dried out in an electric oven of 110 C for 24 hours. The geometry of the specimen was 50x10x200 (mm). 

High-CjS chnkers are employed in the production of high early strength Portland cement (corresponding to ASTM Type HI cemerrt). To produce such cement, the clinker. 

RHC Rapid-Hardening (or High Early Strength or High Initial Strength) Portland Cement / Portlandzement mit hoher Fruhfestigkeit/schnellerhartend... 

HSC High Strength Portland Cement/Portlandzement mit hoher Festigkeit/hochfest... 

Another product purporting to be natural cement was actually a rapid-setting, high-strength portland cement-calcium aluminate cement mixture. This type of material is inappropriate for restoring historic masonry and concrete, as it is likely to distress relatively soft historic masonry substrates. 

Combinations of lignite flyash from North Dakota and hydrated lime can increase the strength and durabiHty of soils. The lime content varies from 2—7% and 1ime flyash ratio from 1 1 to 1 7 (61). Lignite flyash can also be used as a partial replacement for Portland cement to produce strong, durable concrete (62). 

In concrete, triethanolamine accelerates set time and increases early set strength (41—43). These ate often formulated as admixtures (44), for later addition to the concrete mixtures. Compared to calcium chloride, another common set accelerator, triethanolamine is less corrosive to steel-reinforcing materials, and gives a concrete that is more resistant to creep under stress (45). Triethanolamine can also neutralize any acid in the concrete and forms a salt with chlorides. Improvement of mechanical properties, whiteness, and more even distribution of iron impurities in the mixture of portland cements, can be effected by addition of 2% triethanolamine (46). Triethanolamine bottoms and alkanolamine soaps can also be used in these type appUcations. Waterproofing or sealing concrete can be accompUshed by using formulations containing triethanolamine (47,48). 

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. 20.3. The setting and hardening of Portland cement. At the start (a) cement grains ore mixed with water, H. After 15 minutes (b) the setting reaction gives a weak bond. Real strength comes with the hardening reaction ( ), which takes some days.

There are less exotic ways of increasing the strength of cement and concrete. One is to impregnate it with a polymer, which fills the pores and increases the fracture toughness a little. Another is by fibre reinforcement (Chapter 25). Steel-reinforced concrete is a sort of fibre-reinforced composite the reinforcement carries tensile loads and, if prestressed, keeps the concrete in compression. Cement can be reinforced with fine steel wire, or with glass fibres. But these refinements, though simple, greatly increase the cost and mean that they are only viable in special applications. Plain Portland cement is probably the world s cheapest and most successful material. 

R. A. Allakhverdiev, B. Khydyrkuliev, and N. V. Reznikov. Plugging solution for repairing oil and gas wells-contains plugging Portland cement, isobutanol, water and liquid metal alloy of gallium, indium and tin, to increase strength of cement stone. Patent SU 1802082-A, 1993. 

V. A. Blazhevich, D. A. Khisaeva, and V. G. Umetbaev. Plugging solution—contains Portland cement, Uquid waste from soda production and water and has reduced hardening time and increased strength. Patent SU 1776762-A, 1992. 

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