JPS6316355B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to mixed cementitious materials used in the production of glass fiber reinforced concrete. Glass fiber reinforced concrete (hereinafter referred to as GRC) is expected to be widely used as a building material and other uses due to its excellent performance, but the reinforcing glass fibers are eroded over a long period by the strong alkalinity of cement, and It has the disadvantage that the impact strength deteriorates significantly over time, and the effect of the glass fiber reinforcement, which has been painstakingly reinforced, weakens. In order to overcome this drawback, a number of alkali-resistant glass fibers and alkali-resistant coating methods for glass fibers have been proposed in recent years, but none of them have been sufficiently effective. In addition, as a method to compensate for the lack of alkali resistance of alkali-resistant glass fibers, for example, JP-A-53
In the invention of No. 30632, by adding an active silica substance of 0.45 or less, gypsum of 0.40 or less, and a glass fiber deterioration inhibitor of 0.04 or less to cement, the bending strength and impact strength are lower than the initial strength even after one year of production. Although it is stated that there is no strength deterioration in concrete products, there is no mention of long-term strength deterioration exceeding one year, and recent research has shown that the strength deterioration of glass fibers in concrete products reaches saturation within one year. However, it has been revealed that it will not be completely saturated even for two to three years. From this point of view, the inventor of the present application has researched a mixed cement that will not corrode the glass fibers in GRC over a long period of time, and has invented a combination and blending ratio of cement and admixtures suitable for that purpose. This is disclosed herein as the present invention.
The gist of the present invention is that for 1 part by weight of ultra-fast hardening cement,
0.4% of at least one admixture selected from fly ash, volcanic ash, clay, clay and silica powder.
This is a mixed cementitious material characterized by adding ~9 parts by weight. The characteristics of the present invention are that the cement is made of ultra-fast hardening cement that has a low CaO content and relatively low alkalinity, and that can improve strength at an early stage, and that an admixture with a low content of alkaline substances such as CaO is used at a weight ratio of 2 to the cement.
This is a mixed cement containing ~9 parts by weight, an unprecedentedly large amount, and the admixture reacts with the excess alkali in the cement, preventing erosion of the glass fibers by the alkali and reducing the residual strength 20 years after manufacture. The goal is to make it possible to dramatically improve the strength of the product compared to conventional GRC and guarantee product strength for a long period of time. Another feature is that since the residual strength is large, the thickness of the product can be reduced, making it possible to reduce weight and save materials. Yet another feature is that in addition to the above-mentioned savings in materials, it is possible to significantly reduce material costs by adding a large amount of admixtures that are cheaper than cement. The ultra-fast hardening cement used in the present invention is
Calcium haloaluminate known from No. 39924: 11CaO・7Al ₂ O ₃・CaX ₂ (X is halogen)
It is a super fast-hardening Portland cement containing 1 to 30% by weight of sulfate, and has been commercially available in Japan for about 10 years under the trade name Jet Cement. An example of its composition is shown in Table 1. To,
Compared to ordinary Portland cement, the chemical components are
It has a composition that is low in SiO ₂ and CaO and contains large amounts of Al ₂ O ₃ and SO ₃ .

[Table] Since the admixture used in the present invention is added to react with excess alkali in cement, CaO is added to the admixture itself, such as in blast furnace slag.
Those containing a large amount of ash have no effect, and are selected from fly ash, volcanic ash, clay, clay, and silica powder. Since these admixtures contain a small amount of CaO and a large amount of SiO ₂ , the SiO ₂ reacts with excess CaO in the cement to form CaSiO ₃ and fixes the excess CaO, thereby preventing deterioration of the glass fibers. Therefore, the admixture should contain 20% or less CaO by weight, preferably 5% by weight.
% or less is better. In addition, these admixtures also serve as bulking agents, so fly ash, volcanic ash, white clay, and clay are preferable in terms of price. Among them, fly ash has a round particle shape, so it can be used to form cement even with a small amount of water compared to other admixtures. This is particularly preferred since it improves the fluidity of mortar. Further, the particle size of these admixtures is preferably as fine as possible in order to speed up the reaction with excess alkali in the cement, and although the particle size is preferably 100 mesh or less, there is no need to specifically limit the particle size. Regarding the reason for limiting the mixing ratio of admixtures: If the admixture is less than 2 parts by weight per 1 part by weight of ultra-fast hardening cement, the effect of adding it will be poor, especially I.
The value of S (Izotz impact strength) is not sufficient. Moreover, if it exceeds 9 parts by weight, the IS will increase, but the LOP (proportional bending strength limit) value at the 2-week strength during the 2-week curing period will become low, and deformation will easily occur during handling such as demolding and transportation. 2 to 4 parts by weight is preferred. Furthermore, when producing GRC using the mixed cement of the present invention, aggregates, water reducing agents, and setting regulators may be added to the ultra-fast hardening cement and admixtures as necessary, and reinforcing glass fibers may be added. It can be added in a weight ratio of 0.3 to 10% to cement mortar. As the glass fiber, alkali-resistant glass fiber is preferable. In addition, the molding methods used for GRC products include the Primix cast method and the direct spray method. GRC using the mixed cement of the present invention is different from GRC using cement or mixed cement other than the present invention.
When compared with the initial strength, the LOP value and
Although it is inferior in MOR (flexural strength to failure) value, it is equivalent in LOP value after a 28-day immersion test (referred to as an accelerated test) in water at 70°C, which is equivalent to over 20 years of outdoor exposure.
The MOR value improves slightly, and the IS value improves dramatically. Especially often molded into thin panels
In GRC products, improved impact strength allows for thinner walls, which not only reduces weight but also reduces the amount of raw materials used, such as expensive alkali-resistant glass fibers, and adds large amounts of inexpensive admixtures, making it more effective than conventional GRC products. It also enables significant cost reductions. Examples Table 2 compares the initial strength and strength after an accelerated deterioration test corresponding to over 20 years of outdoor exposure of GRC products of Examples of the present invention and Comparative Examples other than the present invention. To prepare the sample, use 0.6 parts by weight of sand as aggregate, 0.33 parts by weight of water, 0.025 parts by weight of water reducing agent, 0.003 parts by weight of setting regulator (citric acid), and the mixing ratio shown in Table 2 for 1 part by weight of cement. Cement mortar obtained by mixing admixtures according to the conditions and chopped strands of alkali-resistant glass fiber containing 5% by weight of the cement mortar are simultaneously sprayed onto the formwork using a direct spray method to inject glass fibers. Form a cement mortar layer and roll over the glass fiber-containing cement mortar layer to defoam and blend the glass fibers into the cement mortar to a thickness of 10 mm.
After adjusting the shape, harden it and remove it from the mold.
I got a GRC board. After curing this GRC board for two weeks, it was cut into a suitable size and used as a sample. The cement used for sample preparation was a mixture of ultra-fast hardening cement and ordinary Portland cement with the chemical components shown in Table 1.

【table】

[Table] Fly ash and blast furnace slag with chemical components shown in Table 3 were used as materials.

[Table] When measuring strength, an autograph was used to measure LOP (proportional bending strength) and MOR (bending strength to failure) at a displacement rate of 3 mm/min.
IS (Izot impact strength) measurements were carried out using an Izot impact tester. In addition, in Table 2, the strength before the accelerated test is the 2-week strength of the sample prepared by the above method, and the strength after the accelerated test is 70°C after the above cutting.
This is the strength after being immersed in water for 28 days and dried. Samples Nos. 1 to 8 in Table 2 are mixed cements in which ordinary Portland cement is used as the cement and fly ash is added as an admixture in increasing proportions. Samples Nos. 9 to 12 are mixed cements in which blast furnace slag is used as an admixture. cement. Samples Nos. 13 to 19 are ultra-fast hardening cements in which fly ash was gradually increased, and Nos. 13 to 17 used mixed cements with mixing ratios outside the present invention, and Nos. 18 to 19 used mixed cements with mixing ratios according to the present invention. This is a GRC manufactured by In order to discuss the superiority and inferiority of ordinary cement and ultra-fast hardening cement, we compared samples Nos. 1 to 8 and 13 to 19 with the same fly ash mixing ratio.
Although the values and MOR values are almost the same, the IS value after the accelerated test is significantly superior to those using ultra-fast hardening cement, especially when 30% or more of fly ash is added. Furthermore, when comparing samples No. 9 to 12 and No. 15 to 19 with fly ash and blast furnace slag used as admixtures, it is found that the LOP value before the acceleration test does not show a decreasing trend in the samples containing blast furnace slag as an admixture; The IS value after the test was low, and the effect of adding the mixture material was not seen. As is clear from the above, GRC using the mixed cement of the present invention has excellent impact strength, especially after a long period of time has elapsed after production. The numbers in parentheses in Table 2 are LOP, MOR,
For each characteristic of IS, the values of sample No. 1 before the accelerated test are
This is the index when it is set to 100.

Claims (1)

[Claims] 1. A glass fiber characterized in that 2 to 9 parts by weight of at least one admixture selected from fly ash, volcanic ash, clay, and silica powder is added to 1 part by weight of ultra-fast hardening cement. Mixed cementitious material suitable for the production of reinforced concrete. 2. The mixed cementitious material according to claim 1, wherein at most 1 part by weight of sand is added as an aggregate to 1 part by weight of the cement admixture. 3. The mixed cementitious material according to claims 1 and 2, in which 0.3 to 10% by weight of alkali-resistant glass fiber is added to cement mortar, which is made by adding water to cement, admixtures, and aggregates. .