JPH0253206B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for transporting hydraulic cementitious compositions such as mortar and concrete (hereinafter referred to as mortars). [Prior Art] Currently, in Japan, almost all on-site concrete is mixed at ready-mix concrete plants (ready-mix concrete plants), loaded onto truck agitators, and transported to the casting site. However, due to the progress of the hydration reaction of cement in mortar, slump loss occurs during transportation, resulting in a decrease in workability, so there is a time limit between the time it is prepared and the time it is poured. In recent years, cure retarders have been developed to suppress deterioration of workability during transportation, but it has generally been difficult to adjust the hydration time. For this reason, there was a natural limit to the time and distance for transporting mortar. [Purpose of the Invention] This invention was made in view of the above circumstances, and its purpose is to propose a method for transporting mortars that suppresses the progress of hydration reactions and enables long-term transportation or long-distance transportation. There is something to do. [Structure of the Invention] This method of transporting mortar involves adding granular ice instead of mixed water to cement or cement and aggregate, etc., and the granular ice gradually melts, and the cement or cement is mixed around the wet granular ice. It is characterized in that it is stirred and mixed with aggregate etc. sprinkled on it, and then transferred to the transportation process when granular ice remains and a macroscopically homogeneous mixed system is formed. In this transportation method, when preparing mortar, granular ice is added instead of water and mixed with cement or cement, aggregate, etc. in a solid phase. Granular ice has cement or cement, aggregate, etc. attached to its surroundings, and becomes like particles sprinkled with powder.
They are dispersed to form a microscopically heterogeneous but macroscopically homogeneous mixed system. During this mixing process, the granular ice is surrounded by powder and covered with a heat insulating layer, which slows down the melting and reduces free water to suppress the hydration reaction. Following this mixing process, when the granular ice remains and forms a macroscopically homogeneous mixed system, it is stored in the drum of a truck mixer vehicle or the like and transferred to the transportation process. During this transport process, the presence of granular ice prevents temperature rise, reduces free water, and suppresses hydration reactions. At the same time, the granular ice gradually melts during this transport process, but the melt water diffuses and wets the surrounding cement or aggregate, creating a microscopically homogeneous mixture where no granular ice remains by the time of pouring. It can be transferred to other types of mortars. The temperature of the macroscopically homogeneous mortar mixture obtained by adding and mixing granular ice instead of mixed water is influenced by the outside temperature, the ratio and temperature of granular ice added, the ratio and temperature of other materials, the insulation properties of the mixing tank, etc. However, by adjusting these conditions appropriately, it is possible to easily produce mortars at a temperature close to 0°C in the presence of granular ice. If there is a large proportion of granular ice remaining at the time of transfer, the low temperature maintenance time will naturally be longer and the hydration reaction can be suppressed for a long time, but if even a small proportion remains, the mortar temperature will be at a low temperature close to 0°C. In addition, since the heat of fusion that prevents temperature rise is retained as latent heat, mortar can be maintained at a low temperature for a long time compared to the conventional case of simply transporting low-temperature mortar, and the object of the present invention can be achieved. Mortar is usually loaded into the drum of a truck mixer and transported to its destination. However, when transported at high temperatures or over long distances (for long periods of time), the materials may be covered with a heat insulating material or stored in a space such as a drum of a mixer truck cooled by a cooling device. The melting time of ice is highly dependent on the temperature of the granular ice and the ice diameter. For this reason, the ice temperature and ice diameter are appropriately selected in consideration of outside air temperature, transportation time, etc., and the time until melting is controlled. In order to adjust the ice diameter to a predetermined value, the granular ice can be sieved and used as necessary. The granular ice may be used by crushing ice cubes at a predetermined temperature, or may be used by deep cooling granular ice to a predetermined temperature. Furthermore, cement aggregate and the like can be cooled in advance and mortar can be prepared. In addition, with this transportation method, it is preferable to supply the entire amount of water required for the hydration reaction of cement as granular ice, but since sand and other aggregates usually contain some moisture, Mixed water with the water removed will be supplied in the form of granular ice. [Function] This method of transporting mortar involves stirring and mixing the granular ice with cement, aggregate, etc. sprinkled around it during the mixing process, which suppresses the melting of the granular ice and maintains a low temperature. Since there is little melt water at the beginning, the hydration reaction can be suppressed to a low level. This state continues in the transportation process after mixing, and the remaining granular ice reduces free water, prevents temperature rise, slows down the hydration reaction, and suppresses a decrease in slump value. The macroscopically homogeneous mixed system formed by the addition of granular ice during the mixing process can easily transition to a microscopically homogeneous mixed system as the granular ice melts, so it is often carried in the drum of a truck mixer during the transportation process. Even if granular ice remains under such conditions, it will not affect the uniformity of the mortar during pouring. [Example] Example 1 Granular ice (-2℃)/cement (20℃) at 0.3/
Samples immediately after mixing (), samples left at room temperature (26-28℃) for 1.5 hours after mixing (), samples left at room temperature (26-28℃) for 2.5 hours (), and comparison. For example, water at room temperature,
Immediately after mixing samples () of cement paste mixed with cement (mixing ratio 0.3/1) were filled and sealed in styrofoam insulation boxes with an internal dimension of 10 x 10 x 10 cm and a thickness of 30 mm, and the center temperature was measured. . The results were as shown in the graph. The curve () shows a sample () of a macroscopically homogeneous mixed system in which granular ice remains immediately after mixing, and the sample was able to maintain a temperature below freezing for a long time, significantly delaying the hydration reaction. Curves () and () are the curves for samples () and (), respectively, where the same sample as sample () was left at room temperature for 1.5 hours and 2.5 hours, and the temperature rose to 2℃ and 16℃ as the granular ice melted. be. The curve () is that of the comparative sample (). According to this graph, the granular ice remaining in the cement paste is difficult to melt, and if it is placed in an insulated box like the sample () (equivalent to transportation under favorable conditions), it will maintain a temperature below freezing for a long time. It can be seen that the hydration reaction can be significantly delayed. In addition, even if the samples () and () are left at relatively high temperatures (corresponding to transportation under adverse conditions), the temperature at 2℃ after 1.5 hours is 2.5℃.
After hours, the temperature only rose to 16°C, indicating that it takes time for the remaining granular ice to melt. For example, if the temperature at the time of cement paste placement after transportation is specified to be below 35℃ or 40℃,
Samples (), (), and () can be transported for a significantly longer time than sample (). For example, if the temperature rise from mixing to pouring is specified to be 20℃ or less, and ignoring the differences in conditions between samples, samples (), (), (), and () are respectively about
The transportation time will be 10 hours, about 6.5 hours, about 4 hours, and about 2.5 hours. Example 2 In Example 1, the sample was stored in an insulated box, and the progress of the hydration reaction was investigated by increasing the temperature; however, in this example, the sample was stored in an open container, left at room temperature, and left under the influence of outside temperature. The progress of the hydration reaction was investigated. Table 1 shows the test conditions, and Figure 2 shows a correlation graph between elapsed time and sample temperature. Granular ice (−
Samples () with ice remaining after kneading at 2°C),
() takes 1.83 hours and 1.08 hours to reach 0℃. On the other hand, for samples () and () using water (0°C) as the mixing water, the temperature rose immediately after kneading.
Remarkable progress of the hydration reaction was observed. In other words, the remaining granular ice takes a considerable amount of time to melt, and during that time it maintains the low temperature, reduces free water, and suppresses the hydration reaction. A similar trend to the relationship between () and sample () was confirmed.

〔Effect of the invention〕

The present invention is as described above, and this transportation method suppresses a decrease in the slump value of mortar during transportation,
Good workability and quality of mortar can be maintained. In addition, the supply area of mortar manufacturing plants such as ready-mixed concrete plants will be expanded, and it will be possible to improve plant operation rates and streamline mortar placement work in remote areas.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are graphs of the correlation between elapsed time and temperature for the cement pastes of Example 1 and Example 2, respectively.

Claims (1)

[Claims] 1 When transporting mortar, granular ice is added to cement or cement and aggregate instead of mixed water, and the granular ice gradually melts, and cement or cement and aggregate, etc. are added around the wet granular ice. A method for transporting mortars, which is characterized in that the mortar is stirred and mixed in a covered state, and then transferred to the transport process when granular ice remains and a macroscopically homogeneous mixed system is formed.