Laboratory report, water/cement ratio - Essay Example

Given below is the graph which shows the relationship between water/cement ratio and compressive strength of concrete. It can be observed from the image that the relationship is hyperbolic in nature. Figure 1: Relation between strength and water/cement ratio of concrete The compaction of concrete is the process adopted for expelling the entrapped air from the concrete (Shetty 2010). Higher the amount of air entrapped, lower is the workability of the concrete. Even wet cement i.e. concrete with high water/cement ratio is not favourable because it can cause voids when the water dries from the pores.

Compaction thus becomes essential in the process of preparation of concrete. 100 percent compaction is necessary to ensure zero percent voids. There are chiefly four methods of compaction and they are as follows: Hand Compaction – Rodding, Tamping, Ramming etc. Compaction by Vibration – Internal, External, Table Vibrator, Platform Vibrator, Surface Vibrator, Vibratory Roller etc. Compaction by Pressure and Jolting Compaction by Spinning In our experiment, we have adopted hand compaction and compaction by vibration using vibration table.

We performed hand compaction by tamping it with a tamping rod and packing the constituents tightly in the mould. Compaction by vibration is the most efficient method of compaction and gives best results for low water/cement ratio concrete. Where only a concrete of a desired strength is required, it can be obtained by compaction by vibration of leaner mixes than possible with hand compaction, thus making the process economical. The demerit of hand compaction of concrete is that it can only be done in unimportant concreting works.

It cannot be used for compaction of high-quality concreting. Also, hand compaction is subjective to the individual performing it and the compactive effort may vary from person to person. The demerit of compaction by vibration table method is that it can be used only for small prefabricated RCC members. From figure 1, we can find that high water/cement ratio is required when concrete is hand compacted as compared to the case when the concrete is vibrated. It can also be seen from the graph that when the water/cement ratio is below the practical limit, the compressive strength decreases sharply.

The compressive strength is calculated by dividing the load at failure with the surface area of the cube. EQUIPMENT The various equipments and materials that were required in the experiment have been listed as following: 20 moulds of 100mm 2 tamping rods 1 vibration table 1 mixer 1 wheelbarrow 1 measuring cylinder Trowel Metal scoops Compression Testing Machine MATERIALS Cement CEM1 Water Sand Coarse Aggregate PROCEDURE 1. We will take the quantity of cement, sand and aggregate in the following proportions: Cement CEM1 1.

70 kg Sand 3.40 kg Coarse aggregate 5.10 kg (natural coarse aggregate) 2. We will add the contents in the mixer and then add the required water by calculating it from the water/cement ratio. 3. We will take out the concrete and put it into the 4 moulds. 4. In 2 out of the 4 moulds, the compaction will be done by vibration through the vibration table while in the other 2 moulds by hand. 5. The moulds are left for curing for 14 days. 6. The cubes are then tested for compressive strength in the compression testing machine. 7. The reading of the load at which the cube fails is noted down and plotted