Masonry cements. Sometimes called mortar cements, these are, typically, mixtures of portland cement
and hydrated lime and other materials that improve workability, plasticity, and water retention.
Packaging and Shipping
Cement is shipped by railroad, truck, or barge either in standard sacks weighing 94 pounds or in bulk. Cement
quantities for large projects maybe stated in tons.
Storage
Portland cement that is kept dry retains its quality indefinitely. Store sacked cement in a warehouse or shed that is
as airtight as possible. If no shed is available, place the sacks on raised wooden platforms. Place the sacks close
together (to reduce air circulation) and away from exterior walls. Cover sacks to be stored outside for long
periods with tarpaulins or other waterproof coverings so that rain cannot reach either the cement or the platforms.
Rain-soaked platforms can damage the bottom layers of sacks.
Cement should be free-flowing and free from lumps at the time of use. Sometimes sacked cement that is stored
develops what is called warehouse pack. This is a slightly hardened condition caused by packing sacks too tightly
or too high. Such cement still retains its quality and is usually restored to free-flowing by rolling the sacks on the
floor. However, if the cement contains lumps that are difficult to break up, test the cement to determine its
quality. Hard lumps indicate partial hydration that reduces both the strength and durability of the finished
concrete. Partially hydrated cement must not be used in structures where strength is a critical factor. Store bulk
cement in weatherproof bins.
WATER
Purpose
Water has two functions in the concrete mix, to effect hydration and to improve workability.
Impurities
Mixing water should be clean and free from organic materials, alkalies, acids, and oil. As a general rule, potable
water is usually suitable for mixing with cement. However, water containing many sulfates may be drinkable, but
it makes a weak paste that leads to concrete deterioration or failure. Water of unknown quality can be used if
mortar cubes made with it have 7- and 28-day strengths, equaling at least 90 percent of the control cubes made
with potable water. Test batches can also determine whether or not the cement's setting time is unfavorably
affected by water impurities. Too many impurities in mixing water can affect not only setting time but can cause
surface efflorescence and corrosion of the steel reinforcement. In some cases you can increase the concrete's
cement content to offset the impurities.
AGGREGATES
Characteristics
Aggregates make up from 60 to 80 percent of concrete volume.
Their characteristics influence
the mix proportions and economy of the concrete considerably. For example, very rough-textured
or flat and elongated particles require more water to produce workable concrete than do
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