Admixtures

The main parameter which influences the strength of any concrete product is the water to cement ratio of the concrete. If you want to make strong and dense concrete, you have to use a low water to cement ratio.

To achieve a manageable or workable concrete with the reduced water to cement ratio, you can use a water reducing admixture (low, mid or high range) in the concrete. The water reducing admixture will compensate for the lack of fluidity in the mix caused due to the lower water to cement ratio.

Sika 1 is an integral waterproofing admixture in Sika’s European product range, I am in Sika US and we do not have this product here. But reading the technical data sheet of the product I do not think adding any color additive in the cement mortar screed is going to have a negative influence on it. But if you are looking for a white colored mortar screed, you will have to use a white cement in the screed instead of grey cement or adding any color additive.

Another alternative would be to use pre-packed water-proofing mortars available in the market specifically made for such applications. These finished products could be purchased in white or grey color.

The rate of strength development of concrete depends on factors such as the water to cement ratio, cement type, use of any mineral admixture and the curing temperature.

From a published research article, the rate of development of the strength of concrete made with ordinary Portland cement and having a w/c of 0.40 is 18%, 54%, 78% for 1, 3 and 7 days respectively of the 28 days strength, considering the 28 days strength as 100% strength.

Whereas for an ordinary Portland cement concrete having a w/c of 0.60, the 1, 3 and 7 days strength is 12%, 42% and 58% of the 28 days strength, the 28 days strength again being considered as 100% strength.

This means that as the water to cement ratio of the concrete reduces, the rate of development of strength of the concrete with respect to the 28 days strength increases.

For concretes made with plain cement the strength gain after 28 days is not very high. For concretes containing fly ashes or slags used as cement replacement materials, the strength continuous to grow beyond 28, 56 and 90 days due to the pozzolanic reaction.

The rate of development of strength during cold season is slow.

I wish your question was in more detail. But, I guess you are probably talking about concrete surfaces which are washed by a water jet the day after it has been placed to expose aggregates.

Concrete surfaces are primarily exposed either for architectural purposes or during mass concreting, when concrete is placed in layers (eg. dams) and one needs a better interlocking between concrete layer is being placed and the previous layer.

Washed concrete surfaces are rough to touch. While washing, typically the cement-sand paste around the coarse aggregate gets washed and the coarse aggregates are exposed.

The depth up to which the concrete surface can be exposed would depend on the amount of surface retarder applied on the formwork or the concrete surface and the pressure at which the concrete is washed. The depth of exposure is generally around 4 to 10 mm and water pressure while washing is around 5 to 10 N/mm2.

David,
There are several options to protect steel in concrete from corrosion. Using concrete made with low water to cement ratio and containing slag or fly ash is good amounts will offer good resistance against corrosion. The cementitious content of concrete should contain atleast 25% Class F flyash or 40% slag for good results. Addition of a corrosion inhibiting admixture to the concrete will also offer resistance to concrete. A calcium nitrate based admixture is the most widely used corrosion inhibitor in concete. You can use a plasticizer or superplasticizer to compensate for the loss in workability due to low w/c ratio. Using epoxy coated steel will also help.

Lowering w/c ratio and using materials like flyash and slag will not only protect the concrete from corrosion but also a host of other durability issues such as sulfate attack, lower permeability, alkali silica reaction etc. and make the concrete really long lasting.

There are several protective coatings available in the market to protect pipes made with only steel. You should contact a local construction chemical company and tell them your problem, they should be able to recommend you the chemicals admixtures and coatings for your need.

If you are a small producer and do not want to add fly ash and slag in the concrete separately, there are also cements available in the market which already contain either flyash or slag in them, you can use these cements.

Check prices with 2-3 suppliers to get an idea about the cost.

Good-luck