JPH03285858A - Cement composition for spraying application - Google Patents

Abstract

PURPOSE:To easily obtain a kneaded material in which the desired composition is held by applying dry blending to materials other than aggregate and water in the compositions of concrete and mortar to form a cement composition and supplying this cement composition to a kneading stage by means of a concrete mixer. CONSTITUTION:A cement composition is obtained by subjecting 2-25 pts.wt. pozzolan powder, 0.05-0.20 pts.wt. short fiber of synthetic fiber, and 0.03-0.40 pts.wt. powder of synthetic resin swelling and dispersing in water to dry blending with 100 pts.wt. normal or high early strength portland cement. By using this cement composition, shotcrete in which the desired composition is precisely kept can be easily obtained at the time of preparing the shotcrete in the job site, without causing loss of the short fiber as reinforcement. Accordingly, the occurrence of splash loss, crack, sagging, etc., at the time of spraying can be prevented, and also cracking due to shrinkage in the course of hardening and after hardening can be reduced.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a premixed cement mixture used when making W4 concrete or mortar for spraying. By mixing, ready-mixed concrete has good sprayability.
The object of the present invention is to provide a cement mixture from which green mortar can be easily obtained.

[Conventional technology]

Conventionally, it has been well known that shotcrete and shotcrete mortar, which are mainly made of Portland cement, aggregate, and water, have been used to reinforce and protect slopes and the inner surface of tunnels.

Mix organic and inorganic reinforcing short mH in the mortar composition,
Furthermore, it is generally known that a synthetic resin adhesive component is mixed together with the reinforcing short fibers to improve sprayability, strength of the cured coating layer, and the like.

For example, in Japanese Patent Application Laid-open No. 59-88352, vinylon short m miscellaneous is added in the composition of shotcrete and mortar from 0.5 to 1.
It was shown that 3 kg/cm was mixed, and JP-A-60-15
Publication No. 1263 states that 1 for ordinary portland cement.
A spray mortar is disclosed in which carbon dioxide (wt%) and aggregate are dry mixed and this is kneaded with a diluted aqueous solution of styrene-butadiene rubber latex. A mixture of synthetic resin emulsion and 11AH is shown.

[Problem to be solved by the invention]

The spraying mixed with the reinforcement 11IIi mentioned above is concrete.

Mortar is usually mixed with cement,
It is prepared by adding short mH together with aggregate, adding a predetermined amount of water, and kneading. However, uniform dispersion of short fibers is generally difficult, and especially when a synthetic resin emulsion is added together with water, the liquid phase Since the viscosity increases, it is necessary to extend the cross-mixing time, and there is a problem in that non-uniform fiber mixing often occurs.

If the above-mentioned non-uniform IJiN mixed concrete and mortar are sprayed, the quality of the coating will be unstable, and some short fibers will easily dissipate during spraying with compressed air, reducing construction efficiency. However, since the above-mentioned cross-conducting work using the concrete mixer is carried out at the work site, there are many problems such as the fact that short fibers having a light specific gravity tend to be scattered by the wind and cause a considerable amount of loss.

[Means to solve the problem]

The present invention is an aggregate in coarse concrete and mortar.

A cement mixture is prepared by dry mixing the ingredients except for water in advance.
By supplying it to the mixing process using a concrete mixer, we succeeded in solving the above-mentioned conventional problems (in the following explanation, part 1% is based on weight).

That is, the present invention uses 5 to 5 parts of pozzolan powder to 100 parts of ordinary or early strength Portland cement.

The gist of this invention is a cement composition for spraying construction, which is characterized by dry mixing 0.05 to 0.20 parts of short synthetic fibers and 0.03 to 0.40 parts of water-swellable and dispersible synthetic resin powder. In the summary, fly ash powder is used as pozzolan powder, and as short fiber of synthetic fiber,
Fiber length is 10-25mm, aspect ratio is 40-250
This includes the use of polypropylene or polyvinyl alcohol-based filaments, and the use of ethylene acetate beer-based or polyacrylic acid ester-based powders as the water-swellable and dispersible synthetic resin powder.

Usually, in shotcrete and mortar, the amount of ordinary or early-strength Portland cement used is 300 to 450 kg per 1 kneaded mixture. 15-112.5k
(]/v/, the short iiem of the synthetic fiber is 0.15 to 0.
9k(J/- will be mixed.

The above pozzolan powders include diatomaceous earth and silicate clay.

Natural powders such as Cristobal, fly ash.

Although known powders such as artificial powders such as slag can be used, fly ash powder is preferable from the viewpoint of quality. Concrete by the addition of this pozzolan powder.

It is possible to reduce the amount of water required to obtain mortar spraying softness (slump value of 0 to 30 m), but if pozzolan powder exceeds 25% of cement, strength development will be delayed, and depending on the environmental conditions, This is unsuitable because the ultimate strength will be lowered, and if it is less than 5%, the water reduction effect will be slight and the effect of reducing the shrinkage rate of the cured layer cannot be expected. Therefore, the most preferable mixing amount is 10 to 20% based on cement.

Short SaW synthetic fibers include nylon, vinylon, polypropylene, polyester, etc.

Any material with excellent chemical resistance can be used effectively, but vinylon and polypropylene filaments are particularly preferred.
These short Ti&H filaments have a fiber length of 10 to 25 mm and an aspect ratio of 40 to 25 for kneading and reinforcing effects.
0 short fibers are preferred.

The water-swelling and dispersible synthetic resin powder used is one that can easily become an adhesive emulsion in the presence of water, which also improves adhesion when spraying concrete and mortar, and increases the interfacial adhesion between the mortar matrix and $1111. In addition to increasing the reinforcing effect of 1m fibers, it also produces a water-reducing effect together with pozzolan powder.This also enables the use of highly hydrophobic polypropylene IiM, and further improves the water retention of concrete and mortar. , a film is formed on the outer surface of the sprayed construction layer to suppress dehydration caused by the ground and transpiration of water from the surface, creating a curing effect.
Therefore, spraying can produce effects such as increasing the strength of the layer and reducing cracks.

In order to obtain the above effect, the appropriate mixing ratio of water-swelling and dispersible synthetic resin powder is 0.03 to 0.40% to cement;
Preferably it is 0.05 to 0.10%.

If the amount of water-swellable and dispersible synthetic resin powder mixed with cement exceeds 0.40%, the viscosity of concrete and mortar will increase and the amount of air content will increase due to crosstalk, and air bubbles will remain in the layer during spraying, resulting in increased strength. Not only does this cause problems such as lowering the amount of water and makes pumping difficult, but it is also uneconomical.

Furthermore, if the amount of the water-swelling and dispersible synthetic resin powder mixed with the cement is less than 0.03%, the above-mentioned effects will be extremely small and the practicality will be insufficient.

Under the quantitative usage conditions of cement, pozzolan powder, and water-swellable dispersible synthetic resin powder as described above, the short I of synthetic 1iAt11
The appropriate mixing amount of M is 0.05 to 0.20% based on the cement, and in particular, 0.05 to 0.10% can provide a practically sufficient reinforcing effect.

Moreover, if the mixing amount exceeds 0.20%, it is difficult to obtain uniform dispersion in concrete or mortar, and not only no particular improvement in effectiveness is observed, but also it becomes difficult to handle.
If it is less than 0.05%, the reinforcing effect will be extremely small, and both are inappropriate.

[Effect]

As mentioned above, the cement formulation for spraying of the present invention is made by uniformly dry-mixing ordinary or early-strength Portland cement, pozzolan powder, short synthetic fibers, and water-swellable dispersible synthetic resin powder in a specific quantitative ratio range. Therefore, it can be easily produced using an internal mixer without scattering loss of the short fibers, and this dry mixing causes the water-swellable dispersible synthetic resin powder and the short fibers of the synthetic sui to become electrostatically charged. Under the tendency of mutual adsorption, a stable homogeneous mixed state is obtained as a whole.

When the cement mixture in this state is kneaded with water and aggregate by a concrete mixer at the construction site, it is possible to achieve the desired mixture without causing almost any separation and scattering loss of short IIN due to wind etc. It is possible to easily obtain homogeneous concrete and mortar that maintains the ratio.In particular, spraying with conventional reinforcing fibers mixed in improves workability due to the small amount of short fibers mixed in compared to concrete and mortar. Spraying that exhibits equivalent or higher strength, crack resistance, and durability can form a reinforcing protective layer.

〔Example〕

The raw materials in the following weight proportions are put into a closed drum mixer with counter-rotating stirring blades and dry mixed to create a cement mixture for spraying.

Ordinary Portland cement 100 parts Pozzolan powder (fly ash powder) 15 parts Synthetic fiber short W
4 Miscellaneous (*1) 0.1 part Water-swellable dispersible synthetic resin powder (*2>, 0.05 part *1. Manufactured by Unitika,
Vinylon filament 250[), 15+an+cut*2. Vinyl acetate copolymer resin powder 2, manufactured by Hoechst Gosei Co., Ltd.
Particle size: 80 mesh or less Pack the above cement mixture into 40 kg bags, send to a spray construction site, and use a concrete mixer to mix 1 part of the cement mixture, coarse aggregate (gravel with a maximum size of 15 gems)
1 part of fine aggregate (river sand) and 0.55 parts of water were mixed together to produce ready-mixed concrete for spraying with a slump value of 20 rIl.

This ready-mixed concrete was sprayed with a compressed air gun using a concrete pump to spray concrete onto a surface lathed onto a tuff bed surface, and the amount of concrete bounce was less than 4% on slopes up to 706. It was about 10% in the vertical plane.

After 28 days had elapsed since the above-mentioned spraying work, the measured values of the strength test were as follows for a test piece in which a part of the concrete layer was cut out.

For comparison, a concrete test of the same material age was carried out using ordinary Portland cement, the same aggregate as in the example, the same cement-to-aggregate ratio, and a cement-water ratio of 0.60 to achieve the same construction softness. Measurements for pieces ()
Shown inside.

Compressive strength kQf/ad 215 (20g) Bending strength 35.8 (32,5) Tensile strength
' 23.5 (19,0) Example 2 Polypropylene filaments (250 manufactured by Chisso Co., Ltd.
D 15mm cut) 0.1 part water-swellable dispersible synthetic resin powder polyacrylic acid ester resin powder (manufactured by Dainippon Ink and Chemicals, trade name Watersol p Q-56s,
Average particle size 50 μs) 0. A cement formulation was obtained in which part f was replaced.

Add river sand to the above cement mixture at a sand-cement ratio of 3.5.
4.0. 4.5, and each of them is the water-cement ratio.
Nine types of mortar A were prepared at 55%, 60%, and 65%.

For comparison, except for the polyacrylic acid ester resin powder blended in the above cement formulation, 9 kinds of mortar B with the same sand-cement ratio and water-cement ratio as above, and ordinary Portland cement in the same ratio as above were used. Nine types of mortar C were prepared by adding river sand and water.

The above mortars A, B, and C were sprayed onto a test formwork with a plywood board surface inclined at 45° using a small blow-flow type mortar gun, and test pieces were taken from each.
Mortar Bending strength (kQf10+/): Bending strength of mortar (kQf10+/): Shotting is not possible (soft joint, small surface adhesion, large sagging) Mortar A using the cement mixture of the present invention was compared to the comparative example Excellent results were shown for B and C.

Furthermore, the cement-sand ratio of the mortars A, B, and C mentioned above is 1:
4.0. In the case of a water-cement ratio of 60%, when we measured the length change of the hardened test piece material (base material age 2 weeks), as shown in the diagram in Figure 1, mortars A and B were compared to mortar C. The shrinkage was significantly smaller, and this was recognized to be mainly due to the hardening caused by the addition of pozzolan powder.

In addition, if a cement mixture is prepared using early-strength Portland cement in place of the ordinary Portland cement in the above-mentioned example, it will have the same effect as described above, as well as ensure good construction in accordance with the weather conditions during construction. It goes without saying that it can be done.

〔Effect of the invention〕

The cement mixture for spraying of the present invention can easily maintain the desired composition without causing loss of reinforcing short fibers when preparing sprayed concrete or sprayed mortar at the construction site. The spraying process prevents warpage loss, cracking, and dripping during the curing process.
Spraying, which reduces shrinkage cracks after curing and has excellent durability, can produce effects such as being able to form a protective layer during construction with a relatively small amount of reinforcing materials mixed in. .

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the subsequent material age and shrinkage rate of a test piece with two turns of base material age. Figure 1: Mortar spraying is the result of measuring the change in length of mortar Material (week) Test strip 11: Mortar spraying (after spraying, in 20'C water for 2 days, after 5 days in 20'C water, at 20°C for 7 days) ,RH-
Pre-thatching of 80% of the indoor piping was performed to obtain base length test pieces, and the shrinkage was measured for up to 14 weeks at 20'C and RH-55%.

Claims (1)

[Scope of Claims] 1) 2 to 25 parts of pozzolan powder per 100 parts (by weight) of ordinary or early strength Portland cement 0.05 to 0.20 parts of short synthetic fibers 0.05 to 0.20 parts of water-swellable and dispersible synthetic resin powder 0. Cement preparation for spraying, characterized in that 0.03 to 0.40 parts of the pozzolan powder are dry-mixed. 2) The pozzolan powder is fly ash powder. Claim 1:
Cement formulation for spraying as described. 3) The cement preparation for spraying according to claim 1, wherein the short synthetic fibers are polypropylene or polyvinyl alcohol filaments having a fiber length of 10 to 25 mm and an aspect ratio of 40 to 250. 4) The cement preparation for a cement preparation according to claim 1, wherein the water-swellable and dispersible synthetic resin powder is an ethylene vinyl acetate or polyacrylate resin powder obtained by an emulsion polymerization method.