CS276699B6 - Agent slowing hardening of concrete mixtures and cement mortars - Google Patents

Abstract

Extract from the production of neutral-sulfite pulp is used as a means of deceleration solidification of concrete mixtures and cement mortars.

Description

The invention relates to the use of a retarding agent for setting concrete mixtures in construction.

For larger volumes of concreting, retarding additives are used in concrete mixtures, which facilitate the technological process of concreting, as they create certain time reserves at the beginning of the setting of the concrete mixture. For these purposes, retarding agents composed of inorganic compounds, e.g. oligo- and polyphosphates resp. borates or organic compounds which contain two or more hydroxyl groups, the increase in the degree of polymerisation of these compounds resulting in an increase in the retarding effect (Ž. example of chemistry, 41, 1968, Š. M. Rachianbajev, Š. M. Baš, K on the pouring of organic matter into the sewer of Portland cement, pp. 2618 to 2624). Retarders of this type include e.g. sulfonated polyphenolates (CS 165 645), dextrins (CS 179 736). Waste products from the hydrolysis of polysaccharides (CS 246 018) as well as sodium or calcium salts of lignin sulphonic acid together with alkaline bicarbonates (Gidr. Lesochim. Prom., 4, 1977, VL Popova, NV Gribanova, RG Gimaševa, RK) were also used for this purpose. Bojarskaja, Izmenenie dispgirujuščich svstv lignosulfonatů v procese pererobotki suífitnogo ščeloka, str. Previously used retarders for setting concrete mixes and cement mortars have the following disadvantages: low efficiency, which necessitates overdosing, which results in reduced mechanical strength, introduction of excessive air, which also leads to reduced strength, which must be compensated by increasing cement addition. Another disadvantage is the toxicity of some retarders. In the case of the use of lignin sulphonic acids, it is difficult to isolate them from the extracts, which requires ultrafiltration or the use of ion exchangers.

The essence of the invention consists in the use of an extract from the production of neutral sulphite pulp as a retarding agent for setting concrete mixtures and cement mortars.

According to the invention, the neutral sulphite leachate is an effective retarder of the setting of concrete mixtures and cement mortars at low concentrations of 0.1 to 0.5 wt. ¾ dry matter, based on the amount of cement, without prior treatment. At present, neutral sulphite leachate is a waste product in the pulp and paper industry in the production of semi-pulp in an optical yield of 75 to 80 wt. %; usually contains 40 to 50 wt. % lignin and 30 to 40 wt. % of the polyoses from the flood present in the wood used for processing, the inorganic content of the extract usually being 50 wt. %.

The following examples illustrate but do not limit the scope of the invention.

Example 1

The cement mixture is prepared by mixing 100 kg of cement (PC 8. Bystrica 475), 38 kg of water and 0.50 kg of neutral sulphite extract with a dry matter of 50 wt. % from the production of semi - pulp from deciduous trees (3PC Štúrovo). The mixture was stirred for 2 min (30 rpm) at 20-30 ° C. The setting time was 7.5 hours and the strength after 180 days 73.1 MPa, while the cement mixture prepared without the addition of neutral sulfite extract had a setting time of 5 hours and a strength after 180 days of 62.8 MPa.

Example 2

The procedure is as in Example 1, except that 1 kg of neutral sulphite extract with a dry matter of 50% by weight is added to the mixture. %. The setting time was 8.5 hours and the strength after 180 days 71.2 MPa, while the cement mixture prepared without the addition of neutral sulfite extract had a setting time of 5 hours and a strength after 180 days of 62.8 MPa.

The retarding agent for setting concrete mixtures and cement mortars according to the invention has applications in the construction industry.

Claims (1)

PATENT CLAIMS Use of leachate from the production of neutral sulphite pulp as a retarding agent for concrete mixtures and cement mortars.