Recommendations to use the d-5 admixture
1. Before applying at prefab reinforced concrete it is necessary to select the concrete composition with the D-5 admixture in laboratory in order to determine the optimal proportion with those cements used at the particular plant.
2. For each grade of concrete it is necessary to test one Control Composition of concrete without admixture (which is used in this production), and one Basic Composition of concrete with 3 % of the D-5 admixture of cement weight.
Both compositions are made of the same materials, with the same proportion of the main components (except water) and must have the results of the slump test). The Control and Basic Compositions differ only by the presence/absence of the D-5 admixture and the amount of the mixing water. In compositions with the D-5 admixture the amount of water should be reduced in comparison with the Control Composition by 15-25% or more on average.
3. The D-5 admixture does not require any pre-mixing with water. When making concrete mixture the D-5 admixture is filled into concrete mixer in dry form together with sand or cement. After water addition the composition should be mixed for 30-120 seconds (depending on the type of mixer and the required fluidity of the concrete mixture).
When using gravity batch mixers, the mixing time is increased to 5 minutes or more.
Transportation, pumping and placing of concrete with the D-5 admixture into formwork should be done as usual. The difference is that the concrete with the D-5 admixture has a large water-retaining capacity, does not delaminate, retains its fluidity for longer and is easier to pump.
4. Almost all monolithic construction facilities have the problem of “cold” joints, which are formed in places where breaks in concreting took place, i.e. when the previously laid concrete has already solidified and the newly made concrete mixture is laid on it. After solidification, the place of “cold” joint is already an artificial crack in the body of concrete, as in this place concrete isn’t monolithic. Therefore, water will leak through the concrete in these places.
When using concretes with the D-5 admixture, the problem of leaking “cold” joints is solved in the most radical and reliable way: “cold” joints in concretes with the D-5 admixture do not leak.
To achieve this effect the following simple operations must be carried out:
in case of a break in concreting, the surface of the previously laid concrete in the place of the future “joint” should be cleaned of cement crust, dust and fine particles washed away with water and the concrete be well moisturized;
after a break in the laying of concrete, whether for a few days or a few weeks, the joint in concrete must be sprayed with water to eliminate dust, sawdust and other contamination – only after this can one lay fresh concrete. At the same time if concrete is laid using a concrete pump, it is necessary to ensure that the first portion of concrete (20-30 liters) is lubricated with oil, which is poured by the concrete pump operator, is drained away.
If these requirements are met, there will be high adhesion and splicing at the molecular level between solidified and freshly placed concrete with the D-5 admixture. High waterproofness of the cold joints will be achieved, even if the break in concreting is 30 days or more (however, both solidified and freshly placed concrete must contain the D-5 admixture). Thus, the effect of “self-healing” of through cracks in concretes with the D-5 admixture is evident.
5. In order to obtain waterproof ceilings in flat roofs and various terraces that do not require any additional waterproofing, it is necessary to make a slab of flat roof or terrace from monolithic reinforced concrete with thickness of not less than 220 mm with D-5 admixture at a proportion 3-4% of cement weight. Such floor slabs will have its own high water resistance W16- W20 (reliable primary protection according to State Standard 31384-2017). Microcracks will not develop for the whole thickness of the floor slab due to constant changes of temperature (day-night, winter-summer), so no additional waterproofing will be required. But we recommend protecting concrete with any proofing against solar radiation to avoid excessive drying of concrete.
It is important to know that in case of large floor slabs, it is necessary to arrange contraction joints in places of fracture and every 6 m. In such cases it is necessary to ensure that these joints are waterproof.
It is not allowed to use sand cement screeds with D-5 admixture as the only layer of waterproofing in flat roofs and open terraces, if the bearing reinforced concrete structures are made without D-5 admixture.
Permanent changes of temperature lead to microcracks. As the result waterproofness of the thin sand cement screeds located under the open air is damaged. In such cases it is necessary to provide additional waterproofing, or to make initially the bearing structure of the floor from monolithic reinforced concrete with D-5 admixture at proportion of 3-4% of the weight of cement.
6. In extreme cases when it is not possible to manufacture a concrete with the D-5 admixture at the concrete plant, the only option is to add the D-5 admixture directly to the mixer with the finished concrete. It is completely possible to apply such a method under the following conditions.
First, it is necessary to order a concrete mixture with low fluidity (1-3 cm). Since the D-5 admixture has a high plasticizing effect, then if it is added to the mixer with the finished concrete with P 3- P 4 fluidity (10-20 cm), the concrete mixture will be delaminated, which is unacceptable to use in construction;
Second, before applying such an extreme method of adding the D-5 admixture to a concrete, it is necessary to carry out a real experiment on one mixer. At the same time it is necessary to know the amount of cement in the volume of concrete that is in the mixer. The required amount of the D-5 admixture is calculated on the basis of 2% of cement weight. This amount of admixture is filled into the mixer (it is not necessary to mix with water in advance!). The mixer should spin for 3-5 minutes at high RPM. Then concrete is checked for fluidity and homogeneity. If the concrete becomes the required mobility and homogeneity, it can be used at a proportion of 2% of the weight of the cement. If the concrete mixture is not sufficiently plastic, it is necessary to use the D-5 admixture bringing its proportion to 2.5% – 3% of the weight of cement to obtain the required fluidity of the concrete. If this technology is successfully applied on one mixer, it is possible to apply it to the whole volume of concrete, but with mandatory visual control on each mixer for fluidity of both the initial concrete and the ready-to-use concrete with the D-5 admixture.
We remind you once again that this method can be used only in emergency cases and with constant qualified control over each mixer.