Technical Field

This invention.is concerned with an admixture for cold-weather concrete, which admixture possesses the superior characteristic that early strength gain of concrete at low temperatures is substantially increased without adverse effects on the basic performance of con¬ crete.

In cold-weather concreting, where concrete is placed in cold weather when outside air temperature is at 0°C or under, it is pre¬ scribed for curing to be provided by heating or insulating in order that the concrete placed will not be subjected to frost damage during the initial curing period until the concrete placed attains a compres- sive strength (generally said to be 30 to 50 kg/cm ² ) sufficient to secure resistance against frost damage. However, it is not an easy matter from the standpoint of work loads and facilities to provide curing by insulation or heating at the jobsite where concrete has been placed.

Background Art

Meanwhile, it has been proposed that the above-mentioned curing by insulation or heating during the initial curing period be eliminated or reduced through the use of an admixture with a marked effect in producing early strength gain of concrete at low temperature. Such an admixture is called an antifreezing admixture and calcium chloride is representative of the type. However, the aπtifreezing admixtures presently available are such that at the levels of addition at which effects as antifreezing admixtures can be demonstrated the additions have various undesirable effects on concrete. One is that the basic performance of concrete is greatly lowered. There are also antifreez¬ ing admixtures which cause abnormal setting of concrete rapidly impairing consistency after mixing to markedly lower workability. By basic performance of concrete it is meant here the performance which will be the basis for performance evaluation and design of. concrete which should be inherent to concrete. In tangible terms it

is the performance represented by compress ive strength at 28 days of standard curing. Further, the effects of antifreezing admixtures as anti freezing admixtures are under question and there. are few cases of actual use. Since such an antifreezing admixture greatly lowers the basic performances of concrete, there are countries (for example, Japan) which prohibit large-scale use of antifreezing admixtures.

As mentioned above, there are various problems about placing cold-weather concrete, and except for special projects, it is normal at present for concrete placement work to be discontinued in the cold season. This constitutes an obstruction to year-round construc¬ tion which has been the long-cherished desire of the construction industry, and poses great problems with regard to the economics and construction period of the entire project..

Disclosure of the Invention

This invention has the effect of prominently improving initial strength of concrete at low temperature without harming basic per¬ formance, and comprises an admixture for cold-weather concrete which does not induce abnormal setting even when added in large quantity, which has been perfected upon numerous studies with the purposes of dissolving the various problems of cold-weather concrete and facili¬ tating year-round performance of concreting work, and which it is possible to use at temperatures as low as -10°C to -15°C.

The admixture for cold-weather concrete of the present inven- tion is of the following composition:

(i) One part by weight of a single compound or a mixture of two or more compounds selected from a group consisting of water-soluble salts of sulfonated melamine formalin conden¬ sates (hereinafter abbreviated as SMF) and water-soluble salts of aromatic hydrocarbon sulfonate formalin condensates

(hereinafter abbreviated as ARF), (hereinafter Component No.1), and (ii) One to twenty parts by weight of a single compound or a mixture of two or more compounds selected from a group

consisting of nitrates, nitrites (both water-soluble salts) and urea (Component No. 2). A water-soluble salt of a sulfonated melamine formalin con¬ densate (SMF) mentioned above is a compound of a structure where melamine, of which amino group is partially sulfomethylated, is condensed with formalin, and is a water-soluble powder of molecular weight of approximately 1000 to 5000. This compound is described in Australian Patent No. 263607.

As for water-soluble salts of aromatic hydrocarbon sulfonate formalin condensates (ARF), they are the water-soluble salts of formalin condensates of sulfonated polycyclic aromatic hydrocarbon such as naphthalene and anthracene, and these aromatic hydrocarbons may be compounds with alkyl groups substituted, or an industrial product which is a mixture of various aromatic hydrocarbons (for example, creosote oil).

These SMF and ARF are known as water-reducing admixtures for concrete, while materials comprising the second component of this invention are known as antifreezing admixtures for concrete. SMF and ARF have the effects of reducing unit water contents required to produce prescribed concrete slumps, and concretes to which these are added will have their strengths increased in accordance with reductions in unit water contents. However, the water-reducing effects of SMF and ARF tend to be reduced at low temperatures, and with the addition of only a SMF or ARF, there is no noticeable effect of increased early strength. The effect of addition of only the second component of this invention is that of greatly impairing the basic performance of concrete similarly to conventional antifreezing admixtures, and the early strength-increasing effect is not necessarily great. However, when Component No. 1 and Component No. 2 are added together, synergistic effects which were wholly unexpected are seen in that the early strength gain effect at low temperature is markedly improved, while the basic performance of the concrete is completely unimpaired. Such a synergistic effect is especially prominent when the ratio between Component No. 1 and Component No. 2 is in the range of 1:1-20 (desirably, 1:3-10). It is noted that there are many concrete water- reducing admixtures other than SMF and ARF which are known.. Examples

are lignosulfoπates and hydroxy carboxylates. However, ^" even though such concrete water-reducing admixtures and Component No. 2 are used together, such a prominent synergistic effect as seen with this in¬ vention cannot be recognized. The addition quantity of the admixture for cold-weather concrete of this invention is suitable in the range of approximately 1 to 10% as expressed in terms of percentages by weight based on cement (dosage), and the early strength gain effect is greater the higher the dosage. Dosages considered as suitable will differ depending on the environ- mental temperature of concrete placed, but to indicate general measures, they are approximately 1% at around 0 to -2°C, approximately 2 to 3% at around -5°C, and approximately 7 to 10% at around -15°C. In general, when dosage is high it is desirable for a composition with a high ratio of Component No. 2 to be selected. Further, it is desirable for dosage and composition to be adjusted so that the

* dosage of Component No . 1 will be not less than 0.2%.

The admixture for col d-weather concrete of this invention is ^• added to concrete by introducing into the mixer when mixi ng concrete. Introduction i nto the mixer may be accompl ished in various forms : i n unmodified powder form, as an aqueous solution , or dissol yed in mixing water. Al so, Component No. 1 and Component No. 2 may be charged separately into the mixer.

With concrete to which the admi xture for col d-weather concrete of this i nvention has been added it will suffice to perform simple curing to the extent of keeping it covered with a tarpaul i n after concrete placement, and it i s unnecessary for special curing such as with ordinary cold-weather concrete. During this curing period there will be no adverse effects on the physical properties and strength gai n of concrete after freezi ng even if freezing of concrete occurs during this curi ng period.

Through the use of the admi xture for col d-weather concrete of this invention , it wil l become possibl e to perform col d-weather concreti ng at temperatures as l ow as -10°C (-15°C i n cases) without curi ng by thermal i nsulation or by heating . Col d-weather concreti ng has been made easy by thi s and it has become possibl e for concrete pl acement to be performed throughout the year, something which had -BUREA

been long-sought by the construction industry.

Examples of implementation of this invention are shown below, but this invention is not limited in any way to these examples.

Example 1

The effects in cases of using Component No. 1 and Component No. 2 individually are shown in this example, along with the effects of conventional antifreezing admixtures.

(1) Concrete Materials Used Cement: Oπoda Type 1 portland cement

Fine Aggregate: inu River sand, specific gravity = 2.62,

FM - 2.78 Coarse Aggregate: crushed sandstone, MS = 20 mm

(2) Admixtures SMF: "Melment" concrete water-reducing admixture manufactured by Showa Denko Co., Ltd. Sodium salt of formalin condensate of naphthalene sulfonate (abbreviated NSF) : Kao Soap Co., Ltd., concrete water- reducing admixture, "Mighty" Calcium chloride, ethylene glycol, urea, sodium nitrate, sodium nitrite: reagent extra pure

(3) Mix Proportions of Concrete

Water-cement ratio of 0.50 and sand-aggregate ratio of s/a = 43% were maintained constant and the mix proportions were determined for target values of slump of 15 cm and air content of 4.5 plus or minus 0.5%.

(4) Mixing, Curing and Testing of Concrete

Mixing of concrete was performed in a room of approximately 5°C using a 4-cubic foot tilting mixer. Concrete was cast in molds for cylinder specimens of 10-centimeter diameter by 20-centimeter height and cured for the specified length of time at the speci¬ fied curing temperature while kept in the molds (wrapped in vinyl bags). Specimens finished curing were left standing in a room of 20°C for approximately 3 hours for thawing before performing compressive strength tests. Curing temperatures were of the three levels of 20°C, -5°C and -10°C.

(5) The test results are shown in Table 1.

Table 1

I cn

I

^■ 1-

As is clearly shown by the above table, the addition of a con¬ ventional antifreezing admixture (calcium chloride, ethylene glycol) greatly impairs the basic performance of concrete. (Comparison of strength for 20°C, 28 days with the value for the mix proportion not using an admixture.) The same may be said for Component No. 2 of this invention. Further, conventional antifreezing admixtures cause abnor¬ mal setting to pose a serious problem in using them. Component No.1 of this invention used alone has practically no early strength gain effect at low temperature.

Best Mode for Carrying Out Invention

Example 2 This example shows the effect of admixtures for cold-weather concrete of this invention consisting of mixtures of Component No. 1 and Component No. 2. The materials and testing methods used in testing were all identical to those in Example 1.

The proportions by weight of the components of the admixtures, and the identification symbols of the admixtures are given in Table 2 and the test results in Table 3.

Tabl e 2

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Table 3

I υo 1

o ml

As is clearly seen in Table 3, the admixture for cold-weather concrete of this invention has an early strength gain effect at low temperature which is markedly greater than for the case of Component No. 2 above, while moreover, the basic performance of concrete is not merely unimpaired, but rather, a remarkable effect of improvement is indicated.

Example 3 This example is of tests varying the mix proportions of concrete and the composition of the admixture. (1) Mix Proportions and Materials of Concrete

Table 4

W/C s/a C W S Admx. (X) (*) (kg/m ³ ) (kg/m ³ ) (kg/m ³ ) (kg/m ³ ) Dosage

I 47.1| 47 350 165 837 955 5%

Except for fine aggregate consisting of sand from the Oi River the materials used for concrete were all identical to those used in the tests of Example 1.

(2) The admixture compositions were those given in Table 5.

Table 5

Sodium nitrite 8 4 1 5.6 6 Urea | | |

SMF 2 2 1 2 2

NSF ! 1 i

Th e test results are shown i n Tabl e 6.

Tabl e 6

It may be seen in this example, similarly to the case of Example 2, that the admixture for cold-weather concrete of this invention pro¬ duces excellent effects.

5 Industrial Applicability

This invention may be utilized wherever it is desired to prepare concrete in cold temperatures.