CS238504B1 - Additive to accelerate the increase in strength of cement mixes - Google Patents

Abstract

The strength of cement mixtures, for example concretes made from Portland or slag Portland cement, is increased by an additive consisting, 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 technical aluminum hydroxide AlO·OH, bauxite, tricalcium aluminate or aluminate cement, and/or gypsum and 0.25 to 2 parts of at least one soluble alkali metal salt, such as sodium sulfate, nitrite or nitrate. 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 β-naphthalenesulfonic acid with formaldehyde

Description

This invention relates to an additive for accelerating the increase in strength of cement mixtures based on Portland clinker.

To accelerate the increase in strength of cement mixtures based on Portland clinker, such as Portland cement, chloride additives are used, especially calcium chloride. However, chlorides are not intended for use in reinforced concrete, because they cause corrosion of steel reinforcement. In addition, an aluminate cement additive is used. However, it is known (R. Bárta: Chemistry and technology of cement, Publishing House of the Czech Academy of Sciences, Prague 1961, pp. 906-907) that mixtures of Portland and aluminate cement set very quickly. Free calcium hydroxide, formed during hydration of Portland cement, forms unstable hexagonal calcium aluminate hydrates - Ο^ΑΗθ and CjAH^ with monocalcium aluminate CA, which is the cause of undesirable rapid setting. Rapid setting is a defect in the normal production and processing of concrete mixtures. According to R. Bárta, when the temperature increases above 21°C, C^AH^ is formed during the hydration of aluminate cement, which has a strength up to 50% lower than stable calcium aluminate hydrates.

From the patent application DOS 2 356 637, a binder with accelerated hardening is known, consisting of 60 to 95 parts by weight of Portland cement and with an additive consisting of 5 to 30 parts of aluminate cement, 2 to 20 parts of gypsum or anhydride and 0.2 to 5 parts of a plasticizer based on sulfonated melamine formaldehyde resin. However, the binder according to DOS 2 356 637 has very short setting times and is therefore also not suitable for the production of concrete. If, instead of calcium sulfate in DOS 2 356 637, sodium or potassium sulfate is used according to AO 217 282, the processing time is 2 —

238 504 the workability of concrete mixtures is extended to a certain extent, but the addition of aluminate cement has a negative effect on the development of the demoulding strength of concrete after longer periods of reheating. The negative effect of the addition of aluminate cement on the development of the strength of a mixture of Portland cement is all the more pronounced, the higher the dose of aluminate cement and the higher the temperature and the longer the reheating period. Therefore, aluminate cement itself or its combination with alkali sulphides or plasticizers is not intended as an additive to cement mixtures, the setting of which is accelerated by reheating and which are intended for the production of load-bearing elements and structures. For this purpose, due to the rapid loss of workability of the concrete mixture, various additives consisting of a combination of aluminate cement with other alkali salts, e.g. with sodium carbonate according to British patent 1 253 773, are not intended either.

The elimination of the above disadvantages and improvement of the strength of concretes whose hardening is accelerated by overheating is achieved, according to copyright certificate 221 789, by an additive consisting of a mixture of 0.5 to 12 parts of aluminum oxide and/or hydroxide, 0.2 to 6 parts of alkali metal sulfate and, if applicable, 0.1 to 2 parts of a plasticizer.

Another surprising increase in the strength of cement mixtures based on Portland clinker, for example concretes made from Portland or slag Portland cement, is achieved by an additive according to the invention. Its essence is that it consists, expressed in parts by weight, of 2 to 10 parts of at least one substance, the essential component of which is an oxide and/or aluminum hydroxide and/or calcium aluminate, such as, for example, technical aluminum hydroxide A10. OH, bauxite, tricalcium aluminate or aluminate 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, for example, sodium sulfate, nitrite, or 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 may be produced by simply mixing the individual components if they are prepared in advance in dry powder form, or by grinding the individual components together.

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

Example 1

The following components were used to produce mortar test specimens;

- Portland cement grade PC 400

- alumina cement grade 400, imported from the USSR

- Gypsum shards, basically almost 1/3th gypsum CaS0 ₄ . 2H ₂ 0

- anhydrous calcined sodium sulfate

- potassium nitrate

- sodium nitrite

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

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

- tap water, ready-mixed mortar mixtures made from 1 part cement, 1 part medium standard sand, 0.5 part fine standard sand and 0.4 parts water.

Mortars were made

1/ comparative without additives

2/ comparison with known additives, consisting - of alumina cement - marked as additive A

- 4,238,504

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

- from a mixture of aluminate cement and sodium sulfate, designated as additive C

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

- sodium sulfate in the ingredient marked D

- sodium nitrite in the ingredient marked E

- in the ingredient marked F potassium nitrate

All additives were dosed as a replacement for cement. The doses and composition of all additives are given in the following table 1.

Test samples - cubes with a side of 2 cm were made from fresh mortar mixtures, which were preheated at 80°C. After 165, 24C and 315 minutes of preheating, the compressive strengths of the test samples were tested. The measured strengths are listed in the following table 1.

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

Example 2

The following slurries were made from grade 400 Portland cement

238,504

- 5 1/ comparative slurry without additives 2/ comparative slurry with known additives, marked A, B and C according to example 1

3/ porridge with an ingredient according to the invention, marked D according to example 1.

All additives were dosed as a substitute for cement. During the production of porridge, the ratio of water was observed

--- =0.3 cement ♦ additive / ·

Test samples were made from the mash - cubes with a side of 2 cm, which were pressed as follows;

- 20 minutes of thermal run-up to a temperature of 80°C

- 130 minutes heat resistance at 80°C

After the completion of the pressing, the compressive strength of the test samples was tested. The composition of the additives, their dosages, as well as the measured strengths are given in the following table no. 2.

The results obtained show that the highest strengths were achieved with the additive according to the invention, while the mortar with an increased dosage of additive A (10% aluminate cement) had less than 50% of the strength of the mortar without the additive. The increased dosage with additive D according to the invention caused a slight increase in strength, while the increased dosage of the known additive B resulted in a slight decrease in the strength of the mortar.

Example >

Two mortars were made from 1 part of Portland cement grade PC 400, 1 part of medium-sized standard sand, 0.5 part of the finest standard sand and 0.4 part of water:

- 6 - comparative and without additives

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

Test samples were made from fresh mortar - cubes with a side of 2 cm, which were preheated at 80°C in a saturated steam environment. After 90 minutes of preheating, they were tested for compressive strength. The following strengths were measured:

Comparative mortar..................unmeasurable strength

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

Example 4

The following mortars were made from 1 part by weight of SPC 250 grade slag Portland cement, 1 part of medium-sized standard clay, 0.5 part of the finest standard sand and 0.4 part of water:

'- comparison mortar without additives

- mortars with additives according to the invention, in composition and doses according to table 3.

Test samples were made from the mortars - 2-sided cubes that were preheated at a temperature of 80°C. After the preheating was completed, the compressive strength of the test samples was tested. The measured strengths depending on the preheating time are given in the following table 3.

Example 5

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

- 7 23β 304

- comparative without additives

- with the additive according to the invention designated K, consisting of 6% aluminate cement, 6% gypsum, 1% sulfate and 0.4% plasticizing additive - sodium dinaphthalimide disulfonate, all as a cement substitute.

The molds with test samples with dimensions of 40x40x160 mm according to ČSN 72 2117 were preheated for 2 1/2 and 5 hours at a temperature of 8C°C in a saturated steam environment. After the end of preheating, the test samples were immediately demolded, some of the samples were tested for demolding strength, the rest was stored in dry air (50-70% relative humidity, approx. 20°C) for strength tests after 28, 90, 260 and 456 days (1 1/4 years). The results obtained, shown in Table 4, show that the additive K according to the invention has a positive effect on the development of long-term strengths of preheated mortars.

However, the examples given do not limit in any way the possibility of various combinations of the individual components of the additive according to the invention.

The additive according to the invention can also be made from various combinations of available raw materials, while the doses of individual components can be suitably adjusted according to the properties of the raw materials, the required conditions for hardening of the concrete, for example when accelerating the hardening of concrete by heating according to the temperature and time of heating and the type of cement used.

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

238 S04

Tab

«3 PM · q·Η > and 0 ÍM í> -M q co co r-l > q -P O 43 M O > axJ Φ Cp +3 O . m i-l ro rH * it- oj 21.0 * o OJ -? 25.2 «4- •k O ΓΟ OJ •t σν . OJ o * σ\ OJ O < OJ ·» Lf\ rM WHAT about OJ what •c what r~i OJ * i-l OJ •k <D CM OJ * LOi 04 what * LOi OJ ffl Φ Λ o q gao <D O O and what in CO z—1 r-4 ·> r-4 co •k ΓΟ i-J cn ♦. m r-4 ro ·» O i-4 *4- *1 o OJ m •k CO r-4 WHAT * what 1-1 •H +3 m o q +3 o with 44 ·.;·> > what X3 X) What what q 03 44 Ή 'Cd q q a o p>> .q 2J O i> ·Γ3 what X3 O Λί what what Φ *> •rl q q ·£ φ q >N Φ about a ι-t Φ cq o f>5 XJ CO 03 Ή 0 a N Φ 43 q -H q φ 0 Φ - O o 44 'CD > · o q co 4J Ή those •rl i—i 43 CO 03 ba OH «· i—4 CO q +3 q ® 0 φ o o 44 '<13 > O q o co 44 +3 Ό •h q q ό •rl O ι—1 03 44 q ba q what what q Ή 03 03 ci OH •p 0— 03 q +» q φ 0 Φ o o 44 'Φ ø> o q CO P •rl q •t-4 i-l CO * Mr would o q CD XJ 'Honor 03 03 co o 5> o q XJ 'Ctí 03 bi OJ ·» t— •k q -p q ® 0 CD O O 44 'CD 2 ^tí 44 XJ 'CD O > 03 O ro q -P co •hqqm •rl 03 r-4 44 bi bi oj •k ua ri 03 CO C0 o > o q x> 'Honor 03 ba OH •k t- ·» q -P q Φ o 0 44 Φ '<D about q XJ o o 44 years 'Φ !> q o q q «o CO -p -P ·Η •rl 03 qq •rl XJ r4 44 would be 04 ·> kD 1-4 03 CO CO o > o q • XJ cd 03 cci •k t— • Fr q j4 +> '<D qq Φ r-4 0 Φ Φ 03 About what q About XJ 44 'Φ q > q O co q q co >o +3 ·Η •rl 03 qq •rl X3 ι—1 44 ba and oh * CD r-l 03 CO and ;>> Φ XJ > about what what m q φ Ή Ν·Η H o q a 1 <4 PQ About (=1 W ^{1 111} < a Type of mortar 1 co F>» > ⁴³ 'cd rt q co !> 0 o q ® O -rl ao r $>> 43 r-4 ' 00 a 1 q 'what about q β »>> what > q 00 that rl CO Φ q H rl and xj o ra a 1

238,504

Table 2

Compressive strength in MPa at 80°C overheating at 80 ^U C for 2.5 hours t- •k co OJ •t 5D « <o r-t 50 « r—1 50 CO r-t «k r-l ro O Ol f' ..... - —- .. , Composition and dosage of additive in / weight of cement, as its replacement !>> XJ CO ta M A CU N © X3 d Mr d Φ β © O O Xi 'Φ > O a what Mr •H a •H r-l XI He knows O r-l 03 OH •k r—t CO 3 P d φ S Φ C3 O x! '© ► o a what about p xi •rt 'Φ and d •rt Ό r-t O Xí 03 Ví d d 50 co d About M 03 03 what EC Mr d © β o o o xi '© o ř* xj O '© d d C0 XJ p o •r-t 03 d h d x! what d He knows 03 O r-t Ví ® OJ d P those CD β © O o xi 'Φ > o d co co o +3 í> •rt O d d •Η XJ r-t 'Φ xí ta He knows He knows About OJ r-t r-t ta ta o xi 'Φ d XJ O ra d d d co -P d d m © ta e © knows o CM About Xí r-t 'Φ > CO O d ro co o P > •r-t O d d •r-l X> r-l 'CO Xí 03 Knows '>V 50 OJ etc ω t- o Xi 'Φ d XJ * O d ta P d d 2 £ β ro © d About Ή 03 o -d Vi '© !> oh o d.o.o -p ro •r-l o d > •H o r-t d XÍ XJ '« He knows what About Ví r-t CM 03 r-l Ingredients label 1 n PQ about Q Xí © 3 >03 d co A Jrf 1 OH > Φ About .H ® d o «η o o o CO > Λί 1 CO Ή H d d ro N Cl, O © Or rt 03 'CO ES d © o ř»>>03 XJ > co co W m ¹ ...........— «

Table 3

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Compressive strengths in MPa after heating at 80°C for a time in minutes o OJ m * what <4· ·* kO r—1 LfJ ·» O OJ LfJ JO r-t o * r-4 JOHN cn JES • cn O cn 1 1 M cd ω and p 'honours Φ ffl sj α ø4 O •t O •k r-4 1 φ r-3 O Ό what what ra Or 8 Fh -P a ri o P>> S XJ QJ {> o 'WHAT Ό Jb O 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! Xl >> Ό CO m Ή Fj a N Φ XI 8 o -P xj 'CO Ό « h •H TO and o 3 ra r-l what 8 and play 2 what about •H S4 > O Ή O r-t ra F-t WHAT _M 'cd • h ra Fh oj -p » Vi r-l fcS. CJ e> ·» yes <d om ra about what and 3% aluminum hydroxide 1.2% sodium sulfate, 7.2% gypsum and 3% aluminate cement 0ingredient labeling 1 W H Type of mortar Comparative mortar 1 what Ό CO 8 CO r4 tJ ra ό φ Ή O r-l fh and 'cd and q •h r>> w a >

238,504

Table 4

and? Poo a 3 Ai CO r-t -P i> ω o £ > CD Poo Γ—1 M Cí CE >3 +3 r-l CO those A<f CD i> CD LCi Cd V From m o m in OJ •k i—i ΓΟ ICi oj •k m m O dD OJ O ·« <* OJ o •k O rO o •k r-l 0Ί o ro m About cn •k o Cd o •k o OJ LT\ cn OJ O r ΟΛ co ω cu O Λ Ό r—i r—t •k cd C\J r—1 «k ω OJ dO * Cd m 1 O and σ 2 -2 o o 4 and what Ό > O OJ * «V ω •k o r-4 o •o what co •k Leader r-l CO 1 -2 cd qo ' Li co c ^a ·> o ff| o co oj CO rl o °« \ ^H EARS O 0) M tt -P & r-llCd cd 11Λ r—11 C J OJ m co C— H rl ^r U rl O Cd Cu OJ Ρ*ϊ c— 3 5 _B 2 CO 173 « β >o what T-t o what ø> 'c0 β o Cl o Poo 1 O = 1 Cu w co 2=(-1 2 N Aí About ID 2 Ή T3 r—i O 2 what '2 2 Cu CD 2 Φ '2 r>3 >That's it · 2 > CO rH Li Λ Oh, those Ό CO N by 2 CQ H O 2 Ό

SUBJECT 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.