PREPARING WET CONCRETE AND CONCRETE TEST

ON SITE

Prepared by:

ShahrulAfifi B Zakaria.

Nur Muhammad Kamil B Mohd Izhari.

Preparing Wet Concrete.

What is concrete?

- Concrete is product consist of cement, sand and coarse aggregates and water which is there are mix together in required proportion (ratio).

Cement Sand Coarse Aggregate

(gravel)

Water

Water /Cement Ratio. For normal mix, the amount of mixture for cement, sand,

and course aggregate is measured by ratio of weight or

ratio of volume. However, ratio of weight is most preferable. For

example, a mixture of 1: 2 : 4 means 1 part of cement, 2 parts of fine aggregate and 4 part of coarse aggregate.

In addition, other examples of concrete mixture proportion used to produce the required strength of concrete are 1: 3 : 6 , 1 : 1.5 : 3 and 1 : 4 : 8.

Water use in concrete mixture is based on water/cement ratio which is it is a ratio of weight of water to weight of cement. The chemical reaction between cement and water causes concrete to harden.

Preparing Wet Concrete.

Preparing Wet Concrete.

Mix the cement with sand

Pour clean water on the mixture.

Mix the mixture with the scoop.

Concrete are ready Mix the mixture with the scoop.

Add course aggregate

Concrete Test

Devide into 2 Test:-i. Slump Test

ii. Cube Test. Concrete Slump Test is a one of test that

usually conducted to measure workability of fresh concrete.

Concrete Cube Test is a test conducted to determine the strength of concrete.

Slump Test Equipment And Material.

Frustum

Base Plate

Steel Rod

Steel Ruler

Procedures:

i. Place frustum on the base plate.

ii. Fill the wet concrete mixture in the cone in three equal layers.

iii. Compact each layer 25 times using compacting steel rod and the top surface is struck off by means of a sawing and rolling motion of the tamping rod.

iv. The cone is slowly lifted and observed the slump.

v. Invert the frustum and place it close to the collapsed concrete.

vi. Measure and record the slump and type of slump.

vii. The slump can be measured as shown in the figure.

Slump Test

Result.

-There are three types of slumps that can happen, which are true slump, shear slump, and collapse slump as shown in figure below.

Quality concrete is concrete which experiences true slump. True slump happens because of its cohesiveness and rich mixes. Rich mix is a mixture that has more cement content.

The shear slump happens due to inadequate mix. Inadequate mix means a mixture which has less cement. Shear slump show lack of cohesiveness in the concrete mix.

The collapse slump shows that the mix is too wet and produces low quality concrete.

Slump Test

Cube TestInstrument And Material.

Concrete cube mould of size 150mm or 100mm. It is used for aggregate size of not greater than 40mm and 25mm. Cube mould for test must be made from steel or cast iron with smooth inner surface. Every mould must have steel plate to support and to prevent leakage.

Compacting steel rod with 16mm diameter and 600mm long.

Compression test machine.

Steel Rod

Compression Test Machine

Cube Mould

Procedures. Mould and base plate must be clean and applied with oil

to prevent concrete from sticking to the side of the cube. Base plate is attached to the mould by using bolt and nut.

Fill the cube with concrete in three layers. Every layer must be compacted for 25 times. This

process is carried out systematically and compaction is done uniformly to all surfaces of the concrete. Compaction can also be conducted using machine.

The surface of concrete must be smoothen so it will has the same level with the upper side of the mould.

Cubes which are made at construction site must be covered with plastic cover for a period of 24 hours before the moulds can be dismantled.

After remoulded, the concrete cubes are submerged in water for curing.

Compression strength test must be carried out for concrete at age 7, 14, and 28 days by using compression test machine.

Cube Test

Result.

- The Strength value of each cube must be recorded and compared with the targeted strength value. The purpose of carrying out concrete test on 7th day and the 14th day is to predict whether the concrete could archive the targeted 28th day strength. In general, concrete would have acquired 70% strength on the 7th day.

Cube Test

Reference

Yusop Bin Paal, Werdah Binti Abdul Halim, Sarifah Binti Daud. (Pengajian Kejuruteraan Awam Tingkatan 4),DBP Kuala Lumpur,2005.

Google Image Search. http://en.wikipedia.org/wiki/

Concrete_slump_test.

Thank You.