What are the impurities in aggregates in what way they affect concrete?

The concrete properties depend from many factors. One of them is aggregates quality, which can be defined as an impurity level. The most unwanted materials in fine aggregates are clay and soil particles. These particles can impure aggregates due to irregular sands in quarry and during the digging process.

What may be the consequences of impurities in aggregate?

Excessive impurities in mixing water not only may affect setting time and concrete strength, but also may cause efflorescence, staining, corrosion of reinforcement, volume instability, and reduced durability. In addition, aggregates should be clean and free from any matter that might affect the quality of the concrete.

What is the harmful effect of organic impurities contamination in aggregate?

Besides reactive minerals, aggregates may contain other impurities, such as organic matter, which are harmful to concrete. Organic matter, such as that derived from decaying vegetation, is capable of delaying setting and hardening of concrete.

What do aggregates do in concrete?

Aggregate materials help to make concrete mixes more compact. They also decrease the consumption of cement and water and contribute to the mechanical strength of the concrete, making them an indispensable ingredient in the construction and maintenance of rigid structures.

What are the impurities of sand?

Clay, silt, salts, mica and organic matter are a source of impurities in sand. All sands are generally found to contain some percentage of silt and clay. Mica is easily discernible from its shining surface.

What will happen to the strength of the concrete if impurities such as clay and silt occur in the sand?

Impurities in building sands contribute to reduced compressive strength. Olanitori [9] asserts that the higher the percentage of clay and silt content in sand used in concrete production, the lower the compressive strength of the hardened concrete.

Is a deleterious material in concrete aggregates?

Deleterious materials are essentially the same as those found in coarse aggregates consisting of clay lumps, shale, soft, friable, or laminated particles, vegetable matter, or other objectionable material.

What are deleterious substances in concrete?

The term “deleterious substances’* or “deleterious constituents” has become a common one for describing this class of materials. Deleterious substances are those which adversely affect the concrete in which they are used. These substances may be categorized on the basis of the nature of their harmful effects.

What are aggregates used for?

Aggregates are used in construction to provide drainage, fill voids, protect pipes, and to provide hard surfaces. They are also used in water filtration and sewage treatment processes.

What is the influence of aggregates on concrete properties?

INFLUENCE OF AGGREGATE PROPERTIES ON CONCRETE. Aggregates influence the properties of concrete/mortar such as water requirement, cohesiveness and workability of the concrete in plastic stage, while they influence strength, density, durability, permeability, surface finish and colour in hardened stage. Aggregates are generally classified

What are the organic impurities in sand?

Organic impurities in sand may be either due to decayed vegetation, humus, coal particles, or organic and industrial wastes depending upon the source of the sand. It is generally considered that organic impurities retard the setting of cement and thus have deleterious effect on the strength of concrete or mortar.

What are the harmful effects of materials on concrete?

Organic impurities, clay, silt and crushed dust, salts, unsound particles, and alkali aggregate reactions. Adverse effects of deleterious materials on concrete includes the increase of water demand in concrete, impair bond strength between cement and aggregate, reduce durability, result in concrete popouts, and impair wear resistance.

How to determine aggregate organic content in concrete?

Colorimetric test recommended by ASTM C 40-92 can be used to determine aggregate organic content. The colorimetric test does not show the adverse effect of the organic impurity since high organic content does not necessarily mean that the aggregate is not fit for use in concrete.