Construction

Potential Groundwater Impacts of Dewatering

·        Contamination

Dewatering can cause the advancement of hydraulic gradients that are additionally fundamental for drawing out water towards wells. Dewatering close to a site with a background marked by contamination in groundwater can bring out hydraulic gradients that can convey the dirtied groundwater towards the dewatering framework and cause contamination. By and large, polluted water requires filtration. To evade this issue, the best technique is to introduce screen dividers and vertically separate regions utilizing bentonite seals.

·        Geotechnical Damage

Dewatering can make the ground lose coherence; the result leads to ground settling. If the ground settling is vast, it can harm close by building and structures. When groundwater is removed from the soil, it makes the soil pack and squeeze. It can likewise also caused by small soil & shallow grounds being removed with the groundwater through well.

This effect can be diminished by a better plan and the utilization of good filtration and groundwater treatment that keep the particles from being separated.

·        Impacts on Water Features

Things that depend on the water like rivers, lakes, and springs have a cozy relationship with groundwater and are, in this way, influenced by dewatering and groundwater control by prohibition. It is essential to keep in mind that groundwater and water-dependent things have eco-systems and fill in as territories. An unfriendly impact of these water bodies will have a huge -ve effect on the earth.

·        Water Resource Depletion

When groundwater is removed for longer periods and in huge amounts for personal or commercial use, it can conceivably bring down groundwater levels and reduce yields. This exhaustion brings about a decrease in significant water assets for other people. An answer to this issue can be an artificial recharge method that infuses release from siphon water back in the ground.

Conclusion

It is crucial to perceive and decrease the effects of dewatering and groundwater control on the earth as dependable residents of the world. We should embrace great construction dewatering treatment system design, examination strategies, and better groundwater remediation innovation to alleviate these issues before it is past the point of no return.

The rebound hammer test is a non-destructive test for the strength of concrete for field testing of concrete.

As per the Indian code IS: 13311(2)-1992, the rebound hammer test has the following objectives:

1. To determine the compressive strength of the concrete by relating the rebound index and the compressive strength
2. To assess the uniformity of the concrete
3. To assess the quality of the concrete based on the standard specifications
4. To relate one concrete element with other in terms of quality

The instrument can be used on both horizontal and vertical surfaces. The main point to be noted is that the graph had to be read appropriately. These days, the hammer is equipped with a digital scale to make life easier.

The IS: 13311(2)-1992 elaborates the procedure in a more detailed manner, making it easier for even beginners to understand the concept.

The point of impact should be at least 20 mm away from any edge or shape discontinuity. For taking a measurement, the rebound hammer should be held at right angles to the surface of the concrete member.

The apparatus is placed on the spot where the test is desired. The hammer is allowed to drop freely. After it strikes the concrete surface it rebounds back. The raise of the rebound is recorded. This test is repeated at different locations and the rebound value is recorded.

The compressive value of concrete is obtained by doing a cube test of the test cube of the batch of concrete on which the rebound test is conducted. The value of rebound and compressive strength of concrete is compared and the value of compression is adjudged from the values of compression test and rebound values.

Around each point of observation, six readings of rebound indices are taken 2nd average of these readings after deleting outliers as per IS 8900: 1978 becomes the rebound index for the point of observation. ( This outlaying is a calculation based method, can be discussed on one’s interest).

Now, we will calculate comp. Strength from rebound number. There are three positions of taking reading

1. Vertical Downward:- Weight of Hammer is increasing stress on spring of hammer
2. Vertical Upward:- Weight of hammer is decreasing the stress on spring of hammer
3. Horizontally :- Weight of hammer have no effect on spring.

This is why, there are three graphs in Rebound Number-Compressive Strength graph of Rebound Hammer.

You will have to calculate the strength from the graph as per position of Rebound Hammer.

For Example,

For Vertical Upward position of Hammer

If 15 Rebound number readings are

48,42,43,43,44,44,45,45,45,45,46,47,48,50

, as per IS:8900, Clause 5.1.1(TESTS FOR TWO OR MORE OUTLIERS , AT LEAST ONE OUTLIER AT EACH END), 42 and 50 are Outlaying values.

Removing those, Average Rebound number is 45.27

From the graph( fro Vertical Upward) , Compressive Strength Will be 40.54 Mpa

Steel reinforcing bars are used to enhance the tensile strength of concrete though concrete is weak in tension, and its because both have the same coefficient of thermal expansion. Also, structural steel is used as such to construct steel buildings, which is more easier in erection and is having less strength to weight ratio compared to concrete. Also steel have 100% scrap value.

MILD STEEL REINFORCING BARS

The mild steel bars are smooth and round in shape having diameter ranges from 6mm to 50mm used for small scale construction works.

Mild steel is also known as low carbon steel having 0.1% to 0.25% of carbon. But mild steel is not considered as an alloy steel though it doesn’t contain other elements in it compared to different steel varieties. As carbon content increases, ultimate strength and hardness will increase, but ductility and toughness decreases. Though mild steel contains very little carbon, it is ductile and weldable but having low strength. Also, mild steel is highly prone to corrosion.

HIGH YIELD STRENGTH DEFORMED BARS

High yield strength deformed bars (HYSD) are manufactured under heat treatment followed by either heat rolled or cold twisted for shaping.

HYSD bars moderately resistant to corrosion and the manufacturing process itself cause surface flaws in it. It is heavily weighted, and its transportation cost is high. Residual stress is high and tensile stress is low in HYSD bars that cause deformation.

THERMO-MECHANICALLY TREATED BARS

TMT bars are having much more advantages than hysd bars and nowadays hysd bars are not using.

TMT bars are having a hardened outer core and soft inner core. These bars are passed through water after they get hot rolled, which makes the surface more firm, and the inner core stays warmer itself. Hence core became more ductile, and no deformation process employed like in hysd makes it more strengthened. TMT bars are having soft ferrite-pearlite core with a hard martensitic rim.TMT bars help to reduce steel consumption to 8 to 11% compared to hysd bars. TMT bars are having more corrosion resistive property and is highly flexible than hysd bars. It is highly earthquake resistant with high tensile strength and low residual strength. TMT bars can absorb about 400 to 600°C of heat and highly fire-resistant.

COLD TWISTED DEFORMED BARS

The specifications related to CTD bars are provided in IS: 1786–1985. They are commonly known as TOR steel bars.

TOR is a kind of high adherence steel. TOR bars have surface deformation formed by twisting the steel after lengthening. This imparts high yield strength to steel and furnishes legitimate proper bondage with concrete.TOR is a type of hysd steel, where the steel bars, subsequent to experiencing the required heat treatment process, are cold twisted and distorted.

QUENCHED AND SELF TEMPERED STEEL

These are very much similar to TMT bars where annealing is the process which is not conducted for QST steel manufacturing. These have adequate quality and malleability. QST steel bars are also having the same cross-sectional material of soft ferrite-pearlite core with a hard martensitic rim as that of TMT bars.