Civil Engineering Materials - Chapter 3 Concrete

Factors that affect the workability of concrete. 2. Aggregate Explain.

- Aggregates with smooth surfaces are more workable than roughly textured aggregates. - Roughly textured aggregates show high friction and segregation tendency. - Besides, non-absorbent aggregates are more workable because porous and non-saturated aggregates demand more water than aggregates which are non-absorbent.

Factors that affect the workability of concrete. 3. Admixture. Explain.

- Chemical admixtures can be used to increase workability. - Use of an air-entraining agent produces air bubbles which act as a sort of ball bearing between particles and increases mobility, workability, and decreases bleeding, segregation. - Mineral admixtures like Pozzolan materials such as fly ash and silica fume are also used to improve the workability of concrete. - The use of fine Pozzolan materials also has a better lubricating effect.

Factors that affect the workability of concrete. 5. Time and temperature. Explain.

- Fresh concrete stiffens with time and loss workability though it is not exactly settling or getting strength at all. - After mixing concrete, some water is absorbed by aggregate, some may be lost by evaporation and some may be spent for initial chemical reactions. - High temperature reduces workability and increases slump loss. - Slump loss is less influenced by temperature in stiff mixes because this type of mix is less affected by a change in water content.

Factors that affect the workability of concrete. 1. Water/cement ratio. Explain.

- It is the most important factor of workability. Workability increases with the increase of water content. - We can express the relation in terms of water/cement ratio. - If the water/cement ratio is small, it indicates a high amount of cement which is helpful for good strength. - But the small water/cement ratio is responsible for lower workability. - If proper compaction cannot be achieved, concrete will not be enough strong as desired. - On the other hand, if the water/cement ratio is increased, workability and compaction problem will be solved but there may occur some other problems like bleeding and losing compressive strength. - Hence an optimum water/cement ratio has to be maintained to balance the workability and strength of concrete.

Factors that affect the workability of concrete. 4. Fineness of cement. Explain.

- The workability of non-air-entrained concrete is increased by increasing the cement fineness. - Also, increasing the fineness of cement reduces the amount of bleeding in concrete.

Define concrete.

-Concrete is a composite man-made material that is most widely used in the construction industry. -It consists of a mixture of binding materials such as cement/lime, water, well-graded fine and coarse aggregates, and admixtures. -In a concrete mix, cement and water form a paste or matrix which fills in the voids of fine aggregates and binds them (coarse and fine aggregates) together. -The mixture is then placed in forms and allowed to become hard like stones. -The hardening of the concrete is caused by the chemical reaction between water and cement and it continues for a long time, and consequently, it grows stronger with age. -The strength, durability, and other characteristics of concrete depend upon the properties of its ingredients, the proportion of the mix, the method of compaction, and other controls during placing and curing.

Define fresh concrete.

-Fresh concrete is a mixture of water, cement, aggregates, and admixtures. -The constituent materials should be uniformly distributed after mixing within the concrete mass during handling and placing.

Range of water/cement ratio for proper workability.

0.4 - 0.6

Two factors that the compressive strength of concrete at a given age and under normal temperature depends primarily on.

1. The water/cement ratio 2. The degree of compaction

Properties of freshly mixed concrete (fresh concrete) that can affect the quality and cost of hardened concrete. / Desired of the freshly mixed concrete.

1. The wetness or dryness of the mix that is the consistency or slump. 2. Uniformity of the mix means that the concrete is mixed thoroughly has a standard appearance and all ingredients are evenly distributed. 3. Workability of the fresh concrete that is the ease with which concrete is placed and consolidated.

Factors that affect the workability of concrete.

1. Water/cement ratio 2. Aggregate 3. Admixture 4. Fineness of cement 5. Time and temperature

Define workability of concrete.

For practical purposes, workability implies that the ease with which concrete mix can be handled from the mixer to the finally compacted shape without segregation during placement and compaction. or The ease with which the concrete ingredients can be mixed, transported, placed, compacted, and finished with minimum homogeneity loss. or The property of fresh concrete which is indicated by the amount of useful internal work required to fully compact the concrete without bleeding or segregation in the finished product.

Define hardened concrete.

Hardened concrete is concrete that must be strong enough to withstand structural and service load which is applied to the concrete and durable enough to the environmental exposure.

The relationship between the compressive strength and water/cement ratio of concrete.

Inversely proportional. The lower the water/cement ratio, the greater the compressive strength would be achieved.

The quality of concrete is measured by its...?

Strength and durability.

Define water/cement ratio.

The water/cement ratio can be defined as the ratio of the weight of water with the total weight of the cement that has been used in a certain concrete mix.

Importance on checking the workability of concrete (especially on slump test).

To ensure that the mixture is uniformly distributed after mixing within the concrete mass during handling and placing.

The principal factor affecting the strength of concrete.

Water/cement ratio of the mix.