Admixtures

The answer to this question may be found in the archives of NRMCA. To the best of my knowledge the first patented non-chloride accelerator was introduced around 1980. However, it might have been used earlier that I don’t know about.

It would depend on the type of structure build using the mass concrete. For mass concreting structures like dams, typical admixtures that could be used may include air-entraining admixtures, water reducers, retarding admixtures, surface retarders etc.

The selection of an admixture is also influenced by the things you want to control. If thermal cracking is the primary issue then a low cement factor and the use of a set controlling admixture would be beneficial. If the issue is cold joints during placing then a retarder would be in order. Each set of circumstances has to be evaluated and decisions made based on the end result you are looking for.

When dealing with acid there are at least 3 factors to consider. They are 1) type of acid. 2) strength of solution and 3) the temperature of the acid.

For the most part, silica fume is advantageous because it raises the density of the concrete and helps prevent the penetration of the acid . The primary problem is that the acid attacks the Portland cement causing the concrete to break down.. That having been said probably the best method is to prevent the acid from reaching the cement.

Addition of other supplementary cementitious materials like, Fly ash and Slag in the concrete should help to improve the durability of the concrete against acid attack. The water to cement ratio of the concrete should also be low (use a high range water reducing admixture to achieve this).

If possible in your case, you can also either apply a coating of acid resistance epoxy coating, in case of flooring you can also use a self leveling epoxy flooring or epoxy-aggregate mortar screed as a protective layer on the concrete.

Good luck.

You can increase the workability of the concrete using a “High range water reducing admixture”. A pure retarding admixture will only delay the set time of the concrete and not increase the workability. If you are looking to increase the workability and also maintain the fluidity of the concrete mix for a while you have to use a “High range water reducing and retarding admixture”.

Make sure that the concrete mix has enough fines in the form of sand and cementitious materials or fillers to avoid bleeding and segregation. If needed you can add a viscosity modifying admixture to improve the rheology of the concrete mix and reduce the chances of segregation.

Based on the way you have asked the question, I am assuming that it’s not an existing basement and you are planning to build it new.

There are several systems of basement waterproofing available in the market, internet is a good tool to find them. A general guideline for basement waterproofing would as described below.

For the base concrete slab:

Before casting the base slab, below the base slab on the gravel base, place a 4” thick lean to normal concrete mix. Coat this concrete with a bituminous coating. Lay a sheet of waterproofing membrane and place the base concrete on this sheet.

The base concrete should be of low water to cementitious ratio, if possible use either fly ash or slag in appropriate amounts to reduce the porosity of the concrete. Use a water reducing admixture (mid or high range) to achieve a manageable workability with the low w/c ratio concrete. Addition of latex polymer to the concrete will help the concrete to be more impervious.

For side walls:

If the side walls will be of concrete, use similar concrete which was used for the base concrete. If the side walls are made of blocks, use solid blocks made using a water repelling admixture in it. Use either a water repelling or a integral water proofing admixture in the mortar used for filling the joints. If possible plaster the wall from outside with a cement-sand mortar. Coat the outside of the wall (or plaster) with a bituminous waterproof coating and cover the wall from outside will the waterproofing sheet membrane, if the basement wall is exposed to soil. If you want additional protection you can fill the gap between the outside wall and the solid with a bentonite slurry.

I think this will give you a pretty strong and durable basement structure.