CS238504B1 - Cement mixtures strength increase acceleration admixture - Google Patents

Abstract

Strengthening of cement mixtures, for example, concrete made of Portland or troscortland cement is achieved by an additive consisting of listed in part by weight, from 2 to 10 parts of at least one substance, substantial the component of which is an oxide and / or a hydroxide aluminum and / or calcium aluminate such as technical aluminum hydroxide Aio · OH, bauxite, tricalciumaluminate or aluminate cement, and / or gypsum and 0.25 to 2 parts at least one soluble alkali metal salts such as sodium sulphate, nitrite or nitrate. The composition of the additive according to the invention can be it is supplemented by the addition of 0.15 to 2 parts a plasticizer, for example condensation β-naphthalenesulfonic acid product formaldehyde

Description

The present invention is concerned with an additive for accelerating the increase in strength of Portland clinker cement mixtures.

Chloride additives, in particular calcium chloride, are used to accelerate the strength of the Portland cement clinker mixture, such as Portland cement. Chlorides, however, are not suitable for reinforced concrete as they cause corrosion of the steel reinforcement. In addition, an aluminous cement additive is used. However, it is known (R.Barta: Chemistry and Technology of Cement, Nakladatelstvo CSAV, Praha 1961, pp.906-907) that mixtures of Portland and aluminous cement solidify very quickly. The free calcium hydroxide formed by the hydration of Portland cement forms with the monocalciumaluminate CA unstable hexagonal ketaluminuminate hydrates - Ο ^ ΑΗθ and CjAH ^, causing undesirable rapid solidification. Rapid solidification is a defect in the normal production and processing of concrete mixtures. As the temperature rises above 21 ° C, according to R. Bart, hydration of alumina cement C ^ ^H ^, which has strengths of up to 50% lower than stably calcium aluminate hydrates, is formed.

From the patent application DOS 2 356 637 an accelerated curing binder consisting of 60 to 95 parts by weight of Portland cement and an additive consisting of 5 to 30 parts of aluminous cement, 2 to 20 parts of gypsum or anhydride and 0.2 to 5 parts of plasticizer is known. based on sulphonated melamine formaldehyde resin. However, the DOS 2 356 637 binder has very short setting times and is therefore not suitable for concrete production. If calcium sulphate in DOS 2,356,637 is used in accordance with AO 217 282 sodium or potassium sulphate, the treatment time is 2 -

However, the addition of aluminous cement has a negative effect on the development of the demoulding strength of the concrete after longer warming times. The negative effect of the aluminous cement additive on the development of the strengths of the Portland cement mixture is the more pronounced the higher the aluminous cement dose and the higher the temperature and the longer overheating time. Therefore, the aluminous cement itself, or its combination with alkaline sulfur, or plasticizers, is not intended as an additive to cementitious compounds which are accelerated by overheating and which are intended for the production of load-bearing elements and structures. For this purpose, due to the rapid loss of the meltability of the concrete mixture, various additives consisting of a combination of aluminous cement with other alkaline salts, e.g. with sodium carbonate according to British Patent 1,253,773.

Eliminating the above disadvantages and improving the strength of concretes whose hardening is accelerated by over-heating is achieved according to the author's certificate 221 789 by an additive consisting of a mixture of 0.5 to 12 parts of aluminum oxide and / or aluminum hydroxide, 0.2 to 6 parts of alkali metal sulphate and 1 to 2 parts plaetifier.

A further surprising increase in the strength of Portland cement clinker mixtures, for example concretes made of Portland or Troskoportland cement, is achieved with an additive according to the invention. In essence, it consists, in parts by weight, of 2 to 10 parts of at least one substance, the essential component of which is aluminum oxide and / or hydroxide and / or calcium aluminate, such as for example industrial aluminum hydroxide A10. OH, bauxite, tricalcium aluminate or aluminum nitrite cement, 2 to 10 parts of calcium sulfate, for example in the form of gypsum and / or gypsum, and 0.25 to 2 parts of at least one soluble alkali metal salt such as sulfate, nitrite, or sodium nitrate. Calcium aluminates release aluminum hydroxide upon hydration (Bárta, p.906).

- 5 238 504

The composition of the additive according to the invention may be supplemented by the addition of 0.15 to 2 parts of a plasticizer, for example a condensation product of 4-naphthalenesulfonic acid with formaldehyde. The additive according to the invention can be prepared by simply mixing the individual components when prepared in dry powder form, or by grinding the individual components together.

The advantages of the additive according to the invention are illustrated by the following examples:

Example 1

The following components were used to produce mortar test specimens;

- Portland cement grade PC 400

- Class 400 aluminous cement imported from the USSR

- gypsum Srepy, basically almost black gypsum CaSO ₄ . 2H ₂ 0

- anhydrous calcined sodium sulphate

- potassium nitrate

- sodium nitrite

- medium fraction of standard ball for testing the mortar strength according to ČSN 72 2117

- fine fraction of standard ball for testing the mortar strength according to ČSN 72 2117

- tap water fresh mortar mixtures made from 1 part cement, 1 part medium standard sand, 0.5 part fine standard sand β 0.4 part water.

Mortars were made

1 / comparative without additives

2 / comparison with known additives consisting of - aluminous cement - designated as ingredient A

- 4,238,504

- a mixture of aluminous cement and gypsum, designated as additive Q

- a mixture of aluminous cement and sodium sulphate, designated as additive C

3 / with additives according to the invention consisting of combinations of aluminous cement, gypsum and a soluble alkali salt, the soluble alkali salt used being

- in the additive labeled D, sodium sulphate

- in the additive labeled sodium nitrite

- in an ingredient labeled F with potassium nitrate

All ingredients were dosed as a replacement for cement. The dosages and composition of all ingredients are shown in Table 1 below.

Test specimens were made from fresh mortar mixtures - 2 cm feline cats, which were warmed at 80 ° C. After 165, 24C and 315 minutes of overwhelming, the compressive strengths of the test specimens were tested. The measured strengths are given in Table 1 below.

The results obtained in Tables 1 show that the highest strengths after all the overwhelming times examined were achieved with the mortars with the additives according to the invention, whereas the mortars with the known additives had lower strengths after 315 minutes of overheating than the mortars without the additives.

Example 2

The following Portland slurries were made from Portland cement class 400

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- 5 1 / Comparative slurry without additives 2 / Comparative slurry with known additives designated A, B and C according to Example 1

3) a slurry with an additive according to the invention, designated D according to Example 1.

All ingredients were dosed as cement substitutes. The water ratio was maintained in the production of the slurries

--- = 0.3 cement ♦ additive / ·

A sample of 2 cm feline cats was made from the slurries and was re-heated as follows;

- 20 minutes heat rise to 80 ° C

- 130 minutes heat hold at 80 ° C

At the end of the heating, the compressive strength of the test specimens was tested. The composition of the ingredients, their doses as well as the measured strengths are given in Table 2 below.

The results obtained show that the highest strengths were obtained with the additive according to the invention, whereas the mortar with an increased dose of additive A (10% aluminous cement) had less than 50% of the strength of the additive mortar. The increased dosage with the additive D according to the invention caused a slight increase in strength, while the increased dosage of the known additive B little resulted in a decrease in the mortar strength.

Example>

Two mortars were made from 1 part of Portland cement class PC 400, 1 part of the middle standard sand fraction, 0.5 parts of the finest standard sand fraction and 0.4 parts water:

- 6 - Comparative and without additives

with an additive according to the invention, designated G, consisting of 6 parts by weight of aluminous cement, 1.2 parts of anhydrous sodium sulfate and 7.2 parts of gypsum additive ^- G, dosed at 14.4% by weight as a replacement for the same amount of cement.

Test specimens were made from fresh mortar - 2 cm feline cats, which were warmed at 80 ° C in a saturated steam environment. After 90 minutes of warming, they were tested for compressive strength. The following strengths were measured:

Comparative mortar ................. not measurable strength

Mortar with additive G according to the invention ............................... 4 MPa

Example 4

The following mortars were produced from 1 part by weight of SPC 250 troscortland cement, 1 part of the standard fraction of the standard sheet, 0.5 parts of the finest fraction of standard sand and 0.4 parts of water:

- Comparative mortar without additives

- mortars with additives according to the invention, in compositions and doses according to the tables, y 3.

From the mortars, test specimens were made - cats with 2 c playing and which were warmed at 80 ° C. After the overwhelming, the compressive strength of the test samples was tested. The names of early strengths as a function of warming up time are given in Table 3 below.

Example 5

The following mortars were produced according to ČSN 72 2117, the composition of which corresponded to the quoted cement (Portland cement class PC 400: standard sand = 1: 3, v / c = 0.5)

- 7 23β 304

- comparative without additives

with an additive according to the invention designated K consisting of 6% aluminate cement, 6% gypsum, 1% sulphate and 0.4% sodium dinaphthylmethane disulfonate plasticizer, all as a cement substitute.

The molds with test specimens of dimensions 40x40x160 mm according to ČSN 72 2117 were re-heated for 2 1/2 and 5 hours at a temperature of 8 ° C in a saturated steam environment. At the end of the overwhelming, the test specimens were molded off, the molding strengths were tested on parts of the specimens, and the remainder was stored in dry air (50-70% relative humidity, about 20 ° C) for strength tests after 28.90, 260 and 456 days ( 1 1/4 year). The results obtained in Table 4 show that the additive K according to the invention has a positive effect on the development of the long-term strengths of the overheated mortars.

However, these examples do not limit the possibility of different combinations of the individual components of the additive according to the invention.

The additive according to the invention may also be made from various combinations of available raw materials, the dosages of the individual components may be suitably adjusted according to the properties of the raw materials, the desired concrete hardening conditions, for example in accelerating the concrete hardening.

The use of the additive according to the invention is particularly advantageous where acceleration of hardening and concrete by over-heating is used, for example in prefabrication.

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Tab

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Table 2

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Table 3

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Compressive strengths MPa after pre-heating at 80 ° C for minutes about OJ m * what <4 · · * kO r — 1 LFJ · » ABOUT OJ LFJ JO R-T about * R-4 JO cn JO • cn ABOUT cn 1 1 M cd ω and p 'honor Φ ffl sj α ø4 ABOUT • t ABOUT • to R-4 1 φ R-3 ABOUT Ό co co ra Ή 8 Fh -P and ri o P >> S XJ QJ {> o 'WHAT B Jb ABOUT what '> j what CJ TO <d -p co • h ra Fh h o xi co C 'co> SSJ + »£ o o r-ι and o N X! l >> Ό WHAT m Ή FJ and N Φ XI 8 o -P xj 'CO • H • H TO and o 3 ra R-L co 8 a h ra 2 co o • H S4> O Ή O r-t and F-t WHAT IS _M 'cd •he plays Fh oj -p »Vi R-L FCS. CJ e> · » yeah <d om ra o co and 3% aluminum hydroxide 1.2% sodium sulfate, 7.2% gypsum, and 3% aluminate cement 0tagging of ingredient 1 W H Kind of mortar Comparative Malta 1 what 8 CO 8 CO r4 tJ ra ό φ R O r-l fh and 'cd and q • h r >> w a>

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Table 4

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OBJECT OF THE INVENTION

Claims (2)

An additive for accelerating the strength of Portland cement clinker cementitious compounds, characterized in that it consists, in parts by weight, of 2 to 10 parts of at least one substance, the essential component of which is oxygen and / or aluminum hydroxide and / or calcium aluminate , such as industrial aluminum hydroxide. CH, bauxite, tricalcium aluminate, or aluminous cement, 2% IC parts of calcium sulfate, for example in the form of gypsum and / or gypsum, and 0.25 to 2 parts of at least one soluble alkali metal salt such as sodium sulfate, nitrite or nitrate. 2. The additive according to claim 1, characterized in that it contains C, 15 to 2 parts of a plasticizer, for example a condensation product of [beta] -naphthalenesulfonic acid with formaldehyde or a sulfonated melamine-formaldehyde resin.