HOW TO STORE AGGREGATES FOR CONCRETE

Aggregates, that are used to make concrete – like sand and crushed stone – need to be stored carefully.

If concrete is to develop its full strength, there must be a proper bond between the cement paste and the aggregates. This bond will be impaired if the sand or stone is coated with dirt, silt, or clay. Because in such concrete, when under load, the stone chips get detached, resulting in lower strengths.

Secondly, the impurities in dirty aggregates mix with cement causing a chemical reaction which prevents the concrete from setting and hardening properly. Another effect could be extensive volume change of concrete.

Other impurities like vegetable debris, animal refuse, coal etc, can also impair concrete strength.

• Store aggregates on a clean hard surface if possible. A platform of planks or old corrugated iron sheets, or a floor of bricks or thin layer of concrete facilities storage.

• Piles of sand and coarse aggregates, in different sites, should be kept separate. On a large job it is fixed to compartmentalize these to avoid inter mixing. For the best results in concrete, strength and durability specifications lay down the proper grading of particle size for both sand and coarse aggregate.

• When stockpiling, each consignment should be dropped in the same place to form a pyramid. Again unloading of lorry loads should not be from too high – otherwise the larger particles get thrown beyond the smaller ones, or the very small sets get separated by wind.

• Because aggregates on site are never completely dry, the amount of water to be added per bag of cement must be correctly apportioned. Besides the moisture content in the aggregates, especially sand, varies with changing weather conditions, and also with changing levels in the same stockpile. A wet mix makes a weak concrete, therefore, periodic checking of the aggregate would help determine the proportion of water to be added.

Keep piles as large in area as possible and low in height – up to 1.5 metres is best. Let material stand for 24 hours before using, so moisture settles evenly.

Is sand piles water drains quickly in a vertical direction but slowly on a gentle fall. Consequently, the last 30 cms becomes very saturated. Leave this layer as a drainage layer for the sand above, using the upper part of the pile, which will have a more constant water content.

As we saw earlier, the aggregate must be kept clean. Bidi and cigarette butts, used tea leaves, sugar, leaves and twigs from nearby trees can all slow up the setting of concrete.