JPH0524100B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a low-shrinkage cement for concrete pavements that exhibits extremely low shrinkage properties and good strength development over short periods of time, especially when used in concrete for pavements. Used for concrete pavement of general sidewalks, expressways, farm roads, airports, parking lots, factory premises, etc. [Prior art and its problems] (1) Asphalt pavement Asphalt pavement, which has become rapidly popular in Japan in recent years, has advantages such as being able to be immediately opened to traffic and having high construction efficiency. The load bearing on tires is large and the structure is unstable, and the generation of ruts and asphalt dust is unavoidable due to fluidity under high temperatures and abrasion caused by the use of spiked tires and tire chains in cold regions. There are disadvantages such as (2) Conventional concrete pavement and the cement used In contrast to the above-mentioned asphalt pavement, concrete pavement is structurally superior because the load is distributed by the rigidity of the concrete slab itself, and the local load on the road slab is relatively small. stable. It also has excellent resistance to rutting and is suitable for long-term use. However, since it requires a curing period of about 2 to 4 weeks after construction to develop sufficient strength, it is not possible to open the road to traffic early, and the concrete slab cracks due to drying shrinkage, which deteriorates the aesthetic appearance. Not only does it damage it, but it also makes the car's running performance worse. 5 to 10 m to reduce the occurrence of cracks.
Although contraction joints are provided at equal intervals, rainwater can easily penetrate into the gaps and cause problems such as localized loss of support of the roadbed due to pumping phenomenon. To solve this problem, a method has been adopted in which the joints are filled with asphalt-based material, but not only is the construction complicated, but the joints themselves also make the car ride uncomfortable. On the other hand, for conventional concrete pavement, Portland cement, blast furnace cement, and fly ash cement have been mainly used. According to the Cement Association of Japan method (CAJS H-11), the average drying shrinkage rate of Portland cement and mixed cement specified by JIS is 13 to 15 x 10 ^-4 for ordinary Portland cement and 11 to 12 x 10 for early strength Portland cement. ^-4 , moderate heat portland cement 11
~13×10 ^-4 , B class blast furnace cement 14-16×10 ^-4 , B
Seed fly cement 12~13× ^10-4 , (more than
(RH44%, 20℃, 13 weeks), and none of the conventional road cements can avoid drying shrinkage cracking. [Object of the Invention] In recent years, roller compacted concrete pavement using so-called zero slump concrete, which has a significantly lower water-cement ratio than conventional concrete mixtures for pavement, has begun to be adopted. According to this construction method, the road can be put into service within about 1 to 7 days after construction, and the construction period can now be significantly shortened. However, since concrete pavement originally has a large exposed area, it is susceptible to drying shrinkage, and because this construction method is a rolling compaction method, it is not possible to create shrinkage joints during construction, so drying shrinkage is particularly small. There is a need for cement that also has good short-term strength development, and its early development is strongly desired. In view of this current situation, we aim to provide high-quality and economical concrete pavement by supplying pavement cement that has unprecedented low shrinkage and excellent short-term strength development. [Means for Solving the Problems] Therefore, the present inventors conducted extensive research to develop cement for concrete paving that has low drying shrinkage and excellent short-term strength development.
More than 40% by weight of the gypsum in the cement is anhydrous calcium sulfate, that is, anhydrous gypsum, and the SO ₃ in the cement is 3.0 to 6.0% by weight, and more importantly, the organic shrinkage reducing agent is also extremely It has been found that cements containing small amounts of 0.2 to 1.0% by weight are preferred. Furthermore, to explain the present invention in detail, as the gypsum, for example, anhydrous gypsum alone or anhydrous gypsum 2
Mixtures of aqueous gypsum and hemihydrate gypsum can be used, but in any case it is necessary that anhydrous gypsum be present in the gypsum in an amount of at least 40% by weight. If this anhydrous gypsum is less than 40% by weight, the effect of reducing shrinkage will be reduced, which is not preferable. Further, the appropriate amount of gypsum to be added varies depending on the type of Portland cement and the amount of blast furnace slag or fly ash added, but is 3.0 to 6.0% by weight based on SO ₃ in cement. If the amount of gypsum added is less than 3.0% by weight based on SO ₃ , the expected shrinkage reduction effect cannot be obtained;
Exceeding % by weight is not preferable because delayed abnormal expansion occurs or strength decreases. The anhydrous gypsum used in the present invention may be either natural anhydrite or a chemical industry by-product, and even if it is pulverized simultaneously with clinker during cement production, powder with a Blaine specific surface area of 2500 to 9000 cm ² /g may be mixed with cement. It's okay. In addition, the organic shrinkage reducing agent to be added in advance during cement production is a commercially available lower alcohol alkylene oxide adduct type (trade name: Tetraguard), polyether type (trade name: Hividan), or glycol ether type (trade name: Hibigard). However, it is expensive and is not effective unless it is used in a large amount, usually 3 to 5% by weight based on cement, which is an obstacle to its widespread use. In the present invention, it has been found that by using it in combination with anhydrous gypsum, the effect can be sufficiently expressed even in a very small amount, which would have almost no effect when used alone. Various portland cement clinkers can be used as the base clinker. In normal cases, anhydrous gypsum alone or a mixture of anhydrous gypsum and dihydrate gypsum or hemihydrate gypsum (hereinafter referred to as gypsum) is added to ordinary Portland cement (or clinker), preferably at a concentration of 3.5 to 6.0% by weight based on SO ₃ . However, depending on the construction conditions (especially weather conditions such as temperature and humidity), it is preferable to use early-strength Portland cement (or clinker) or moderate-heat Portland cement (or clinker) with gypsum added. . That is, from the viewpoint of drying shrinkage, moderate heat Portland cement with gypsum added at 3.0 to 4.0% by weight based on cement SO ₃ is preferable, and from the viewpoint of initial strength in addition to drying shrinkage, cement SO ₃ is preferable. It is based on early-strength Portland cement with gypsum added to a standard amount of 3.5 to 6.0% by weight. Further, when using the cement according to the present invention as a normal or early strength Portland cement clinker, blast furnace slag and fly ash can be added. That is, when adding blast furnace slag, the amount of blast furnace slag is 5 to 60% by weight, and the amount of gypsum added is SO ₃ in cement.
The standard content is preferably 3.5 to 6.0% by weight. In addition, when adding fly ash, the amount of fly ash should be 5 to 30% by weight, and the amount of gypsum added should be 5 to 30% by weight.
It is preferably 3.0 to 5.0% by weight based on SO ₃ .
If the amount of SO ₃ is outside this range, the effect of reducing drying shrinkage will be reduced or delayed abnormal expansion will occur.
With regard to the amount of blast furnace slag and fly ash, it is not preferable to exceed this upper limit range because the development of initial strength will be delayed. [Mechanism of action] The feature of the present invention is that hydration reaction occurs with C ₃ A in the cement clinker, and most of it becomes ettrin guide (C ₃ A, 3CaSO ₄ , 32H ₂
A sufficient amount of gypsum to stabilize O) is used together with a very small amount of an organic shrinkage reducing agent of 0.2 to 1.0% by weight. Since the amount of C ₃ A varies depending on the type of cement, there is an appropriate amount of gypsum to be added for each type. For example, the amount of C ₃ A in the moderate heat Portland cement currently produced in Japan is approximately 4% by weight or less, so the weight of anhydrous gypsum required to stabilize all of this as ettringite in the hardened cement body is approximately 6% by weight. %, i.e. as cement SO ₃ approx.
An appropriate value is 3.5% by weight. The amount of C ₃ A in ordinary Portland cement and early strength Portland cement is as high as 7 to 10% by weight, but in this case, if the gypsum calculated to be stoichiometrically stabilized as ettringite is added, Unreacted gypsum remains for a long period of time and gradually generates larger needle-shaped ettringite, which generates an expansion pressure that destroys the hardened structure, causing cracks. Therefore, as a result of repeated research, the appropriate amount of _SO3 for ordinary Portland cement and early-strength Portland cement is 3.5~
The content was 6.0% by weight. For mixed cement with blast furnace flag and fly ash added, the appropriate amount of _SO3 is 3.5 to 6.0% by weight and 3.0 to 5.0% by weight, respectively.
I got it. The reason why anhydrous gypsum was used here as gypsum is that its dissolution rate in water is slower than that of other gypsums, resulting in the formation of coarse ettringite, which tends to form capillary tubes with large diameters. This method utilizes the phenomenon that the property of trapping water synergizes with the effect of an organic shrinkage reducing agent in reducing drying shrinkage. Several mechanisms have been proposed for drying shrinkage of hardened cement. Shrinkage in the medium and high humidity range, which is important in practice, is thought to be due to deformation due to capillary tension caused by the interfacial tension of condensed water existing in an unreacted state in the voids in the hardened cement paste. Capillary tension (q) is the surface tension of condensed water (γ) and the total radius of curvature (r ₁ , r ₂ ) at the water surface at both ends of the capillary.
It is expressed as the product of the sum _of the _reciprocals of The internal stress (σ _cp ) due to capillary tension that affects the deformation of is expressed as the product of the residual condensed water content (We) and capillary tension (q) (formula) σ _cp = We・q … Therefore, in the hardened material In order to reduce the generated internal stress, that is, the drying shrinkage stress (σ _cp ), a great effect can be expected if both the residual water content (We) and the capillary tension (q) can be reduced at the same time, and the present invention makes this possible. This is what I did. Organic shrinkage reducers reduce the surface tension (γ) of condensed water.
It is said that the effect of reducing the capillary tension (q) and thus the drying shrinkage stress (σ _cp ) is reduced. Therefore, its effect only affects the surface tension (γ) of the condensed water in Eq. Here, as mentioned above, coarse ettringite is generated by appropriately increasing cement SO ₃ with anhydrous gypsum, and capillary tubes with a large diameter are formed in the hydrated tissue, and the total radius of curvature (r ) increases, which has the effect of lowering the capillary tension (q). Furthermore, the addition of anhydrous gypsum has the effect of reducing the residual water content (We) in the equation, and as a result increases the concentration of the shrinkage reducing agent in the condensate water, thereby lowering the surface tension (γ) and thus the capillary tension (q), which increases the drying process. It acts in the direction of further reducing the shrinkage stress (σ _cp ).
The reason for this is that ettringite has a very large amount of water of crystallization, so its production acts to digest residual condensed water, and does not incorporate organic shrinkage reducing agents into the crystallized water. As mentioned above, anhydrous gypsum is used as a cement composition, and the content varies depending on the type of cement.
We ensured a sufficient amount of cement SO ₃ to undergo a hydration reaction with C ₃ A to stably produce an appropriate amount of ettringite in the hardened material, and further added an organic shrinkage reducing agent to the extent that it would have almost no effect when used alone. By using only a small amount of , it is possible to provide a low-shrinkage cement for pavements that has an extremely small drying shrinkage of about 40 to 80% compared to conventional cement and has good early strength development. [Example] Next, the present invention will be explained in more detail with reference to Examples. Ordinary Portland Cement Clinker, Moderate Heat Portland Cement Clinker, Early Strength Portland Cement Clinker, Dihydrogypsum (SO ₃ 45.1
%), type anhydrous gypsum (SO ₃ 57.8%), fly ash, blast furnace slag, and an organic shrinkage reducing agent (alkylene oxide type, trade name, Tetragard AS20) were mixed in specified amounts to prepare the cement shown in Table 1. .

【table】

[Table] (1) Examples 1 to 7, Comparative Examples 1 to 7 The drying shrinkage rate of mortar specimens was measured in accordance with CAJS H-11-1981 (Cement Association Standard Test Method). In this case, the mold is removed 24 hours after molding, the base length is immediately measured, and then cured in a constant temperature and humidity room at 20°C and RH 60%. After curing for one day, the basal length was measured, and then a drying shrinkage test was performed using two curing methods in a constant temperature and humidity room at 20°C and RH 60%. These results are shown in Table 2. (2) Examples 8 to 14, Comparative Examples 8 to 11 The drying shrinkage rate of the mortar specimens was measured in accordance with ASTM C 109-86. In this case, after molding
Demold in 24 hours, measure the base length immediately, and then
After curing in a constant temperature and humidity room at 60% RH and 60% ℃, and removing the mold 24 hours after molding, the root length was measured after curing in water at 20℃ for 6 days, and then in a constant temperature and humidity room at 20℃ and 60% RH. Drying shrinkage tests were conducted using two curing methods. These results are shown in Table 2.

【table】

[Table] (3) Examples 15 to 21 As a roller compaction concrete mix, unit cement amount 265Kg/m ² , unit water amount 79Kg/m ² , fine aggregate ratio
After mixing concrete with 47.2% and AE water reducing agent (C x 0.25%), formwork (φ10 x
20 cm, 10 x 10 x 40 cm for drying shrinkage test), and compacted with an electric hammer. The compressive strength specimens were removed from the mold one day after molding and subjected to standard curing. In addition, the specimens for drying shrinkage tests were removed from the mold and lengthened one day after molding, and then cured in a constant temperature and humidity room at 20℃ and RH60%.
The drying shrinkage rate was measured. Table 3 shows the drying shrinkage test results and compressive strength test results.

〔Effect of the invention〕

As can be seen from the above examples, according to the present invention, anhydrous gypsum is used as the cement composition,
It secures a sufficient amount of cement SO ₃ to stably generate an appropriate amount of Etrin guide in the hardened material through a hydration reaction with C ₃ A, which content varies depending on the type of cement, and furthermore, when used alone, it By using an organic shrinkage reducing agent in such a small amount that no effect is recognized, the drying shrinkage is approximately 40 to 80% lower than that of conventional cement.
%, and in concrete mixes for roller compaction pavement, it is possible to achieve a drying shrinkage rate of 4 x 10 ^-4 or less, which is theoretically said to prevent shrinkage cracks.
It is possible to provide a low-shrinkage cement for pavements that exhibits good early strength development. As a result, when a road or the like is constructed using the cement of the present invention, the drying shrinkage is extremely small, so it is possible to make a concrete slab with a large span, and there is almost no need for joints. As a result, the running performance of the vehicle is improved, the source of traffic noise is reduced, the pumping phenomenon is reduced, and the strength develops quickly, so the present invention can be opened to traffic within a few days after pouring.There are many advantages of the present invention. .

Claims (1)

[Claims] 1. 40% by weight or more of the gypsum in the hydraulic cement is anhydrous gypsum, and SO ₃ in the cement is 3.0%.
6.0% by weight and an organic shrinkage reducing agent of 0.2 to 1.0% by weight. 2. A low shrinkage cement for paving according to claim 1, wherein the hydraulic cement comprises normal, early strength or moderate heat Portland cement clinker and gypsum. 3. The pavement according to claim 1, wherein the hydraulic cement is composed of ordinary or early strength Portland cement clinker, blast furnace slag and gypsum, the blast furnace slag is 5 to 60% by weight, and the cement contains 3.5 to 6.0% by weight of _SO3 . Low shrinkage cement. 4. Low shrinkage for pavement according to claim 1, wherein the hydraulic cement is composed of ordinary or early strength Portland cement clinker, fly ash and gypsum, the fly ash is 5 to 30% by weight, and the cement contains 3.0 to 5.0% by weight of _SO3 . cement.