JPH0519499B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides a cement composition for underwater casting, that is, without using a tremie pipe or enclosure, in other words, while allowing dynamic contact with river water or seawater, from above the water to the bottom of the water, etc. Concrete or mortar compositions used for direct pouring. (Prior art and its problems) When a normal cement composition used for construction and construction above or below ground is poured directly into water from above the water, the cement content may be lost during transportation of the cement composition in water. When the water flows out and reaches the place where the concrete is to be poured, such as at the bottom of the water, and even after the concrete has been poured, it is subjected to forces from unexpected directions due to the action of the water flow or eroded, and does not take the desired shape. Furthermore, due to the action of water flow, the cement content is partially lost, especially in the surface layer, and as a result of this, it has traditionally been considered extremely difficult or impossible to create a cement structure with high strength. Ta. In order to overcome this problem, it has recently been proposed to incorporate synthetic or natural polymeric substances as thickeners (West German Patent Application No. 2326647,
JP-A-57-3921, JP-A No. 57-123850, JP-A No. 58-
No. 181754, No. 59-26956, etc.), and cement compositions containing these polymer thickeners are now widely used in underwater construction. This type of cement composition for underwater placement currently in use suppresses the loss of cement to a low level during transportation in water (this can be seen as the generation of turbidity in water), but at the same time When compared with so-called ordinary cement compositions to which no additives are added, there are the following problems. 1) High cost (The main ingredients of currently widely used polymer thickeners are cellulose ethers or polyacrylamide, and in order to suppress turbidity in water below a specified level, the addition rate of this type of thickener is required. That is, the weight percent of the thickener to the unit water amount is 1.5
2) The setting time is delayed (the setting time becomes longer depending on the amount of polymer thickener added, and this is due to the influence of water flow etc. until setting and hardening). (This means that it is difficult to maintain the desired shape due to the addition of polymeric thickeners) and 3) Workability is reduced (as a matter of course, the viscosity of the cement composition increases due to the addition of polymeric thickeners). Therefore, if it is done manually, it will be difficult to handle with a scoop and finish with a trowel, and if it is pumped, the feeding pressure must be set extremely high, which means that the pump load will be high. ). (Objective of the Invention) Therefore, the main object of the present invention is to be able to suppress the outflow of cement components to a low level during transportation in water, similar to the conventional cement compositions for underwater pouring, and to It is an object of the present invention to provide a cement composition for underwater pouring which can significantly shorten the setting time compared to cement compositions for underwater pouring, and therefore develops strength quickly, so that it is not adversely affected by water flow. . Another object of the present invention is to provide a cement composition for underwater casting that has better workability and construction properties than conventional ones. Still another object of the present invention is to provide a cement composition for underwater pouring that is less expensive than conventional ones. (Means and Actions for Achieving the Object) According to the present invention, the above-mentioned object is to provide a cement composition for underwater casting which is mainly composed of cement and has a polymeric thickener added thereto, in which a part of the cement is silica fuyum. This is achieved by replacing. The appropriate amount of silica fume is 5-20% based on the weight of cement, especially about 10%. If it is less than 5%, it will have little effect on shortening the setting time, while if it is more than 20%. 0.1−
This is because the viscosity of the cement composition becomes too high due to the amount of water absorbed by 0.3 μm silica fuyum particles and the thickening effect of silica fuyum itself, resulting in a decrease in workability. This is because, as a result of careful consideration of the workability of the composition, it was found that the optimal blending amount of silica fuyum was approximately 10%. When comparing conventional cement compositions for underwater pouring, if 10% of the cement content is replaced with silica fuyum, setting time in water is reduced by approximately 20-
This can be reduced by 30%, and this is true even when the time required for coagulation becomes longer, such as when a large amount of water is added or when the water temperature is low. According to the cement composition for underwater casting according to the present invention containing silica fuyum, the outflow of cement components in water is suppressed as the mixing rate of silica fuyum increases. For example, a cement composition for underwater casting (a lump for testing) containing 10% (wt%) of silica fuyum, which is the optimum blending ratio for cement, was allowed to fall freely into water, and the relationship with underwater turbidity was investigated. However, the underwater turbidity was 1/2 compared to the cement composition for underwater casting (based on the conventional method) as a control, which differed from the above test lumps only in that silica fuyum was not mixed. ~1/
It was found that the number decreased to 4. This means that if a certain turbidity standard is set, the amount of polymeric thickener added can be reduced in the case of the cement composition for underwater casting according to the present invention. According to the method of the present invention, the addition rate of polymeric thickener can be reduced from about 1.5% in the conventional method to about 1.0%. Although silica fuyum is expensive when compared with cement, it is significantly cheaper when compared with polymeric thickeners, so the above fact shows that the cement composition for underwater pouring according to the present invention is more expensive than conventional ones. This means that it is cost-effective compared to
It also means that the amount of polymeric thickener incorporated can be reduced, resulting in a further reduction in setting time. It should be noted that the cement composition for underwater casting according to the present invention contains silica fuum, but when this cement composition is poured, SiO ₂ in the silica fume and free lime, which is a hydration product of cement, are mixed.
The pozzolanic reaction with Ca(OH) ₂ densifies the internal structure and improves durability (salt damage resistance and freeze-thaw resistance), especially in marine environments. (Test Examples, etc.) Next, the present invention will be specifically explained using various test examples. The cement composition (sample) for underwater casting used in the following test example was prepared by adding water to Portland cement (and silica fuyum) to prepare a cement paste, and adding a polymer thickener (from Daicel Chemical Industries, Ltd.) to this cement paste. A product commercially available under the trade name "Cellcrete H" whose main component is hydroxyethyl cellulose) is added and mixed, based on the cement content of this polymer thickener-containing cement composition. Although this is a mortar in which standard sand is added and mixed in a ratio of 1:2, it should be noted that concrete in which coarse aggregate is added to the mortar can also be subjected to the same test. Reference test example 1 The ratio of water to cement (W/C) is 50%, and the addition rate of polymer thickener (weight % of polymer thickener to unit water amount) is 0.05, 1.0, and 1.5%. When each sample was prepared and the setting time (initial and final) was measured at room temperature (20°C), the results shown in Figure 1 were obtained. The initial setting time for the sample without the addition of polymeric thickener was 4.5 hours, and the final setting time was 7.2 hours.
time, whereas the addition rate of polymeric thickener is 1.5
%, and the setting start time for the conventional standard sample was 10.2 hours, and the end time of setting was 13.5 hours, and both the start and end times were delayed by about 6 hours by the addition of the polymer thickener. There was found. Reference test example 2 Samples with a water-to-cement ratio (W/C) of 55% and various addition rates of polymer thickener were prepared, and about 2 kg of each sample was shaped into dumplings. , a tube filled with tap water (diameter 200 mm, length
After 30 seconds of falling, the turbidity of the water was measured at a position 1200 mm below the water surface and plotted on a graph, and the results shown in Figure 2 were obtained. When the acceptable standard for turbidity is set at 50 ppm or less, it can be seen from the inflection point of the turbidity curve in the graph of FIG. 2 that the addition rate of the polymeric thickener should be about 1.5% or more. Test example 1 The ratio of water to cement (W/C) or the ratio of water to cement and silica fuyum (W/C+F) is 55
%, and the mixing rate of silica fuyum is 0-20%.
Samples varied within the range of (mixed proportion to cement weight) and W/C+F of 55%, polymer thickener addition rate of 1.5%, and silica fume mixing rate of 0- Samples varying within a range of 20% were prepared, and the setting time (initial and final) of each sample was measured at room temperature (20%).
℃), the results shown in FIG. 3 were obtained. From the graph shown in Figure 3, it can be seen that the addition of silica fume has no effect on shortening the setting time for ordinary samples to which no polymeric thickener is added, but when a polymeric thickener is added, the so-called Regarding the samples for underwater casting, it is found that as the mixing rate of silica fuyum increases, the setting time is shortened, that is, the setting time is shortened by about 3 hours at a mixing rate of 10%, and about 5 hours at a mixing rate of 20%. . It should be noted that when the silica fuyum content approaches 20%, the viscosity of the sample composition becomes extremely high, causing difficulty in workability, so from the viewpoint of workability, the silica fuyum content should be kept at about 10%. It was also revealed. Test Example 2 In view of the results of Test Example 1, the mixing rate of silica fuyum was set to 10%, the ratio of water to cement and silica fuum (W/C + F) was 50 and 55%, respectively, and no polymer thickener was used. Samples were prepared with various addition rates, and the coagulation time of each sample was measured at room temperature (20°C). On the other hand, the setting time was similarly measured for a control sample without the addition of silica fume, and the setting time ratio of each test sample was plotted using the control sample's setting time as the standard (1.0), and the results were as shown in Figure 4. was gotten. The coagulation time ratio of each test sample was 0.7-0.8, and it was found that if the silica fuyum content was 10%, the coagulation time could be shortened by about 20-30%. In addition, the sample was prepared by changing W/C+F within the range of 40-50% and by setting the temperature condition to a low temperature range of 5-20℃ (the addition rate of polymer thickener to the test sample was 0.8%).
When the setting time was measured and the setting time ratio was plotted in the same manner as above, the results shown in FIGS. 5 and 6 were obtained. The coagulation time ratio was also about 0.75-8.0 in these test samples, and it was found that the coagulation time could be shortened by about 20-25% with a silica fume mixing rate of 10%. Summarizing the results shown in Figures 4-6, it can be seen that by mixing 10% silica fume, the setting time can be shortened by about 20-30% regardless of the amount of water added or water temperature conditions. Test Example 3 Same as Reference Test Example 2, except that the mixing rate of silica fuyum was not 10%, the ratio of water to cement and silica fuyum (W/C+F) was 55%, and a polymer thickener was added. When the turbidity in water was measured for samples with different ratios, the results shown in FIG. 7 were obtained. From this figure 7, if the turbidity standard is set to 50 ppm, the addition rate of polymer thickener will decrease from 1.5% to 1.1%.
This means that it can be reduced by 0.4%. Test example 4 The ratio of water to cement (W/C) or the ratio of water to cement and silica fuyum (W/C+F) is 50
%, and the contamination rate of silica fuyum is 0 or 10%.
When the setting time of samples with varying addition ratios of polymeric thickeners was measured at room temperature (20°C), the results shown in FIG. 8 were obtained. If we apply the result obtained in Test Example 3, that is, the addition rate of the polymer thickener can be reduced from 1.5% to 1.1%, to the result obtained in Test Example 4, we can see that the polymer thickener It can be seen that the setting time is shortened by about 1 hour as the addition rate of . In other words, the setting time of a sample with a silica fume content of 10% and a polymer thickener addition rate of 1.1% is compared to a conventional sample with a polymer thickener addition rate of 1.5%. Considering the above results and the results shown in Test Example 1, the time will be reduced by about 1+about 3 hours. Cost estimation example Ratio of water to cement and silica fuyum (W/
C+F) is 50%, the unit water amount is 200Kg/ ^m3 , the cement is set to the standard value of 400Kg/ ^m3 , and the silica fuyum mixing rate is 10%. Cement for underwater pouring according to the present invention Regarding the composition and the conventional cement composition for underwater casting when silica fuyum is not blended and the addition rate of polymer thickener is 1.5%, cement: 15 yen/Kg, polymer thickener: 4,500 yen/ The results of cost calculations assuming 60-70 yen/kg of silica fuyum are shown in Table 1 below, and the cement composition according to the present invention can reduce the cost by 1400 yen/ ^m3 compared to the conventional one. found.

[Table] Test Example 5 Ratio of water to cement and silica fuyume (W/
C + F) is 50%, and the mixing rate of silica fuyum is
A 1:2 mortar composition (test product) according to the present invention in which the ratio of water to cement was 10% and the addition rate of polymeric thickener was 1.1%, and a high A conventional 1:2 mortar composition (control product) with a molecular thickener addition rate of 1.5% was prepared, and the manual workability (workability) was investigated. The results are shown in Table 2 below. As shown, it was found that the workability was considerably improved by incorporating silica fume and reducing the amount of polymer thickener used.

【table】

[Table] (Effects of the invention) The cement composition for underwater casting according to the present invention can effectively suppress the outflow of cement components during transportation in water, and can shorten the setting time, so that the strength can be increased quickly. Therefore, it is hardly affected by the adverse effects of water flow. Furthermore, the addition rate of polymeric thickener can be reduced, resulting in further shortening of setting time and cost reduction. In particular, it is formed because the silica fume blended into the cement composition for underwater casting according to the present invention undergoes a pozzolanic reaction with Ca(OH) ₂ , which is a hydration product of SiO ₂ cement, to densify the internal structure. The cement structure has an increased resistance to salt damage, etc., and the cement composition according to the invention therefore has special advantages that make it particularly suitable for use in marine environments.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the addition rate of a polymer thickener and the setting time of a cement composition, and Figure 2 is a graph showing the relationship between the addition rate of a polymer thickener and the setting time of a cement composition. A graph showing the relationship between the addition rate of thickener and water turbidity. Figure 3 is a graph showing the relationship between the mixing rate of silica fuyum in a cement composition and the setting time of the cement composition. Figure 4 is a graph showing the relationship between the addition rate of silica fuyum and the setting time of the cement composition. Figure 5 is a graph showing the relationship between the setting time ratio of a cement composition containing 10% silica fume and the addition rate of polymer thickener, based on the setting of the mixed cement composition. Graph showing the relationship between the setting time ratio of a cement composition containing 10% of silica fuyum and the ratio of water to cement based on the setting time of a cement composition containing no silica fuyum. , Figure 6 shows the relationship between the temperature and setting time of the cement composition, and the setting time ratio of the cement composition containing 10% silica fuum and the setting time of the cement composition, based on the setting time of the cement composition without silica fuum. The graph showing the relationship with temperature, Figure 7, is the same as Figure 2, except that the silica fume content is 10%.
Graph showing the relationship between the addition rate of a polymer thickener in a cement composition and the turbidity in water, expressed as %, No. 8
The figure is a graph showing the relationship between the addition rate of the polymer thickener and the setting time in cement compositions containing 0 and 10% silica fume.

Claims (1)

[Scope of Claims] 1. A polymer thickener mainly composed of cement and hydroxyethylcellulose is added in an amount of 0.9 to 1.2% based on the weight of water used for kneading, and silica fuyum is added based on the weight of the cement. A cement composition for underwater placement, characterized by containing 5 to 20%. 2. The cement composition for underwater casting according to claim 1, wherein the amount of silica fuyum is about 10% based on the weight of cement.