CS221600B1 - Casting cement mass - Google Patents

Abstract

The invention relates to a casting cement mass and its use in construction, in which the volume changes occurring during solidification, hardening and drying of the mass are regulated by means of additives causing expansion. The main components regulating the volume changes are aluminate cement, gypsum and lime hydrate. With their use it is possible to prepare mixtures with constant volume or expansion. Thus, undesirable shrinkage and the risk of cracking of the prepared layer are suppressed.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting cementitious compound and its use in the construction industry in which the additive-inducing additives control the rapid changes occurring during solidification, hardening and drying of the mass.

As part of the introduction of new progressive methods and procedures for finishing works in the construction industry, the technology of self-spreading materials has been developed as a substitute for laborious production of concrete screeds and cement screeds and their smoothing with gravel materials.

The production of such materials is ensured by a number of companies worldwide, such as Periplan 300 by Polychemie GmbH Augsburg or Ardux K 15. These are polymer-based materials. Further, anhydrite-based materials (Konlhydrite) are produced.

Said compositions contain either finely divided fillers or do not contain fillers in the case of Conhydrite. All materials containing limestone or other flours as fillers are characterized by high shrinkage on drying of the solidified and hardened material. As a result, stresses occur in the cured mass which, if exceeded by the tensile strengths, cause the surface to be cracked. This can be avoided either by increasing the tensile strength by adding polymeric substances, such as Periplan 300 or Ardux K 15, or by reducing the shrinkage of the material. This is achieved by adding a coarser filler, as is the case with Ralit. The addition of polymeric substances increases the cost of the mass by about 10 times that of the same mass without the additive. The addition of a coarser filler (grain size up to approx. 5 mm), in turn, deteriorates the self-spilling ability of the material significantly and increases the water release. The anhydrite-based materials do not have shrinkage by drying, but their production is bound to the occurrence of natural anhydrite and it is not in Czechoslovakia.

These drawbacks are overcome by the casting cementitious compound of the invention. The composition is characterized in that, by means of suitable additives, conditions are created for the crystallization of ettringite or gypsum in the already solidified mixture. To suppress unwanted shrinkage, ettringite — a mineral with a composition of 2 CaO is required. AI2O3. 3! GaSO4. . (30 - 32) H ₂ O - developed topochemites, ie practically in solidified matter and not from solution. The resulting ettringite fills pores in the solidified mass and causes expansion. The amount of expansion and the time for which ettringite is formed depends on the amount of the additives according to the invention and their relative ratio. In order to use the casting cementitious mortar according to the invention, ettringite should be formed for a period of 1 week to 1 month after solidification. After a longer period of time, the produced surface contains so little moisture that ettringite formation is very unlikely. The main components controlling volume changes are aluminous cement, gypsum and lime hydrate. With their use, it is possible to prepare mixtures which are stable in volume or expandable. In this way, undesired shrinkage and the risk of cracking are suppressed and the cost of such a mixture is comparable to that of the aforementioned Ralit.

He did

Mixture consisting of:

% limestone # 4% PC 400

2.2% alumina cement

1.5% lime hydrate of cleaner% natural gypsum

0.3% w / w plasticizer based on sulphonated phenol-formaldehyde resins under the name Umaform SF, after mixing with water (water coefficient 0.35), test specimens of 4 x 4 x 16 cm were made with integrated measuring contacts. The specimens were stored for one month in a humid environment according to ČSN 72 2112. The volume changes were measured as changes in the length of the specimens using a surface deformometer. They are expressed in length / mm / m.

After 7 days the length change was + 0.53125 mm / m

After 14 days the length change was + 0.54375 mm / m

After 28 days the length change was + 0.54375 mm / m

Example 2

Mixture consisting of:

% limestone # 4% PC 400% aluminous cement

1.7% lime hydrate pure% natural gypsum

0.3% of Umaform SF powdered plasticizer was prepared in a similar manner as in Example 1. 1 and was subjected to the same tests.

The length change was:

after 7 days + 0.51875 mm / m after 14 days + 0.6125 mm / m after 21 days + 0.64375 mm / m after 28 days + 0.6875 mm / m

Claims (2)

SUBJECT CLAIMS 1. A cementitious compound consisting of from 20% to 70% by weight of Portland cement; 20 to 70% by weight of a finely divided filler, such as ground limestone, type # 4 or type # 6; 0.1 to 2% of a plasticizer and 5 to 20% of an additive for controlling volume changes during solidification, hardening and drying, characterized in that the additive is comprised of 20 to 35% by weight. aluminous cement; 5 OF THE INVENTION up to 30 wt. % pure or dolomitic lime hydrate; and 35 to 60 wt. calcium sulfate. 2. The cementitious compound of claim 1, wherein the calcium sulfate is finely ground natural gypsum or building gypsum, or waste gypsum from titanium dioxide, or waste gypsum from phosphoric acid.