The article on portland cement quality features is prepared in collaboration with Telling Company, the engineering enterprise massively applying hydraulic lime, lime mortar and concrete materials in its projects. The UK-based business concentrates its efforts on residential and commercial architectural, design and engineering projects, collaborating with the industry experts and utilising the most efficient and modern materials.
Portland cement is used mainly for concrete and reinforced concrete structures in the ground, underground and underwater structures, including those that are prone to freeze-thaw. As the first choice solutions portland cements are used only in those cases where there is no cheaper binder alternative – air and hydraulic lime, blended cements and others. When choosing cement it is required to keep in mind introduction of solutions, water-retaining additives – lime, clay, ash, ground limestone, and others. In any case of using portland cement it should be taken into account that there are special versions of this binder – fast curing, plasticized, hydrophobic and white, as well as mixed based on Portland cement or lime-based. In addition, possible to use other kinds of cements, which are also necessary to keep in mind when choosing a sustainable binder for specific construction purposes. They are all in one way or another are discussed below.
Activity, one of the most important indicators of quality of portland cement is the measure of the tensile strength, obtained during the tests of axial compression. In the manufacture of cement mortar the sand containing not less than 98% of quartz with a grain size of 0.5-0.9 mm is utilised. Samples are manufactured according to standard procedure. The type of cement is assigned basing on its activity indicators.
The type of cement is usually called the value of its activity, but rounded to the lower limit, and in view of its flexural strength. Accelerated tests can be initiated to determine the activity, for example at the age of 3 or 7 days, but with the subsequent data revisions in relation to the normal 28-day-old test samples.
Apart from activity basing on the standards, in accordance with the theory of the CSI and its congruence law it is desirable to determine the calculated activity of Portland cement (and other binders). By activity the calculated compressive strength (or with other types of stress state) the optimal structure of cement stone produced and tested with the actual conditions of the claim on the basis of cement is meant. The recorded value of the activity is referred to a the settlement because it is included in the formula for calculating the optimal respective strength of the concrete structure. The standard activity is a conditional factor, needed for cement product marking to compare it with other cement. The technical characteristics of Portland cement include such indicators (in quantitative terms) as: fineness, density, setting time, soundness (according to the visual inspection of samples). All of them are due to their standard procedures determination.