In many ready-mixed concrete terms and conditions they reserve the right to adjust the cement content by up to 20kg/m3 against the mix design certificate. This quite reasonably allows them to maintain the strength in response to their quality control procedure.
Typically concrete masonry units are placed between prestressed or reinforced concrete beams to provide a floor capable of taking domestic loading at ground and upper floors. A levelling screed or structural topping maybe required. Expanded polystyrene blocks (EPS) can also be used between the beams but these have no structural resilience and therefore require a structural screed to transfer loads to the beams. These are proprietary systems and must be installed according to the manufacturers details.
Limestone fines to BS 7979, Specification for limestone fines for use with Portland cement is a fine powder obtained from the processing of limestone.
Corrosion of steel is an electrochemical process with different reactions occurring at the anodic and cathodic sites. A supply of water and oxygen is required to maintain the reaction.
Limits on aggregate water absorption are rare though they may be useful to link to an undesirable concrete property, such as freeze-thaw susceptibility, as water absorption is easily determined. Historically it is not known the source of the limits but the following may be of interest.
Calcium chloride was used as an accelerating admixture in concrete up until the mid 1970s. In the hydrate form it contains about 25% by weight of water of crystallisation. Since this can vary the code of practice current at the time (CP 110: part 1: 1972, Structural use of concrete) specified the amount of anhydrous calcium chloride i.e. the material containing no water. The Code stated that the amount should never exceed 1.5% by mass of cement where the concrete contains embedded metal. This value included that chloride associated with the marine aggregate if used.
Colour variation in concrete is inherent to the constituent materials. Some of these materials are manufactured products (cement, admixtures, pigments) and some are natural (coarse and fine aggregate).
The BS 4027 Sulfate-resisting Portland cement (SRPC) is now not available, however EN 197 has now introduced a Sulfate-resisting Portland cement designated as CEM I-SR 0 or 3. The availability, whether bulk or in bags, is not known.
In the UK the most commonly used lightweight aggregate is LYTAG, a sintered fly ash, also known as pulverised fuel ash (pfa). Other aggregates, made from a variety of raw materials, are shown in the Table below.