JP2008254933A - Reinforced concrete member using foamed resin fine aggregate and receiving bending stress - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a reinforced concrete member lightweight by using a foamed resin while keeping required strength. <P>SOLUTION: The weight reduction and the strength in the reinforced concrete are balanced by making the mix rate of the foamed resin aggregate in the region 11 near the neutral axis of the member larger than that in the margin region 12 of the member, considering that compressive stress is acted on one side of the neutral axis of the cross-section of the member and tensile strength is acted on another side of the neutral axis of the cross-section of the member in the reinforced concrete member receiving bending stress. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reinforced concrete member that is reduced in weight by using a foamed resin such as polystyrene foam as a fine aggregate.

  Reinforced concrete structures are often used because they provide the required strength at a low cost. However, they have the disadvantage of being heavy, and are looking for ways to reduce their weight. In order to further reduce the weight, it has been proposed to use a foamed resin fine aggregate as a lightweight aggregate.

Japanese Patent Laid-Open No. 10-101454 JP 2001-232619 A JP-A-5-837 JP 2000-64493 A Japanese Patent Laid-Open No. 5-4843

  Conventional lightweight concrete using foam resin as an aggregate is mixed with foam resin uniformly or made into a laminate of a layer containing foam resin and a layer without mixture. In order to integrate the laminate dynamically, additional work was required after casting and forming concrete, such as by providing a stopper or using a strong adhesive.

  Moreover, patent document 1 is applied to the foundation of a foundation, and opposes a supporting pressure. Moreover, the layer in which the foamed resin is mixed and the layer in which the mixed resin is not mixed are simply stacked, and only the compressive stress is dealt with, and the bending stress has not been studied.

When foamed resin is mixed as fine aggregate, the strength decreases, so the strength may be insufficient even if weight reduction can be achieved.
The present invention pays attention to the characteristic of bending stress acting on the member and aims to reduce the weight by using a foamed resin while maintaining the necessary strength of the reinforced concrete member that receives the bending stress.

  As shown in FIG. 2, the member subjected to the bending stress is compressed stress on one side and tensile stress on the other, centering on the neutral axis of the rectangular cross section and I-shaped cross section. Focusing on the fact that the stress is increasing, in a reinforced concrete member subjected to bending stress, the mixing ratio of the foamed resin fine aggregate near the neutral axis of the member is made larger than the edge of the member, thereby reducing the balance between weight reduction and strength. Is taken.

  In the reinforced concrete member of the present invention, the use of the foamed resin fine aggregate makes it possible to reduce the weight and obtain the required strength. Utilizing the characteristic that the bending stress is linearly distributed, the mixing ratio of the foamed resin fine aggregate is changed according to the region of the member, so it is possible to rationalize the weight and easily handle even on-site construction. can do. In addition, it is not necessary to prevent misalignment for lamination as in the prior art, and a member having high heat insulation performance can be obtained.

In the present invention, as shown in FIG. 1, a foamed resin fine aggregate is used for a reinforced concrete member 1 subjected to bending with reinforcing bars 2 arranged.
In the region 11 of the neutral axis of the member, the mixing rate of the foamed resin fine aggregate is high, and the mixing rate is lowered toward the region 12 on the edge of the member.

  Laminate concrete with different mixing rates in order. First, concrete with a low or low mixing rate is cast, and concrete with a high mixing rate is placed as it approaches the neutral axis. When the neutral axis is exceeded, the mixing rate is reduced and concrete is placed, and finally the mixing rate is zero.

  In addition to placing concrete in layers, it may be placed by continuously changing the mixing rate with a concrete placing machine capable of changing the mixing ratio.

Experimental Example The foamed resin fine aggregate used was roughly crushed from the waste foam polystyrene with the physical properties shown in Table 1, then reduced to about 1/20 by irradiation with far-infrared rays, and further pulverized to a particle size of 4 mm or less. It is what. Low-strength and low-elasticity foamed polystyrene has become extremely hard due to heat reduction.

Foamed polystyrene waste material for fine aggregates, and early-strength Portland cement for cement, mortar mixer is used to mix cement and water, knead for 60 seconds, pulverized foamed polystyrene waste material is added and kneaded for 120 seconds I did it.
The formulation is shown in Table 2. The water-cement ratio is changed from 30% to 60%, foam polystyrene mixing ratio for each (volume ratio of EPS waste material occupied in the mortar: EPS mixing ratio, or V _EPS display) was changed to 0-60%.

A specimen (40 × 40 × 160mm) for strength test was prepared and compacted with a shaking table and a hand vibrator. After demolding the next day, standard curing (20 ± 2 ° C) was performed, and a strength test (JIS A 1108) was performed at a material age of 7 days.
The relationship between the EPS contamination rate and density is shown in FIG. As the EPS contamination rate increases, the density decreases linearly, and when the EPS contamination rate is around 60%, the density of the mortar is approximately 1.0 g / cm ³ .

  FIG. 4 shows the relationship between the EPS mixing rate and compressive strength, and FIG. 5 shows the relationship between the EPS mixing rate and bending strength. 4 and 5, it can be seen that both the compressive strength and the bending strength tend to decrease with the increase of the EPS mixing rate.

FIG. 6 shows the relationship between mortar density and compressive strength. For comparison, the figure also shows that the volume of waste EPS is not reduced.
From FIG. 6, it can be seen that the strength development at the same density is larger in the mortar using the EPS waste material subjected to volume reduction treatment. This is thought to be due to the increase in Young's modulus of EPS waste due to heat volume reduction treatment. In concrete using heat-reduced EPS, the initial microcracking occurs later than before. It is guessed.

Based on the strength test results, the apparent EPS waste strength was calculated using Bache's equation (1).

  FIG. 7 shows the relationship between the EPS contamination rate and the apparent EPS aggregate strength. The apparent strength of EPS was generally increased by decreasing the water-cement ratio, that is, increasing the matrix strength. In addition, there is an EPS mixing rate where the apparent EPS intensity becomes the maximum value for each matrix strength. Considering this as the optimal mixing rate, the optimal mixing rate decreases with increasing matrix strength.

From the above, the highest apparent EPS aggregate strength was obtained when the water-cement ratio was 30% and the EPS contamination rate was 40%.
Actually, the strength of the EPS waste material does not change, so it was judged that the apparent strength was a condition that the EPS strength could be effectively exhibited in a compounded manner.

Sectional drawing which shows the concept of this invention. Stress distribution explanatory drawing when receiving bending stress. The graph which shows the relationship between EPS mixing rate and mortar density. The graph which shows the relationship between EPS mixing rate and compressive strength. The graph which shows the relationship between EPS mixing rate and bending strength. The graph which shows the relationship between the density of mortar and compressive strength. The graph which shows the relationship between EPS mixing rate and apparent EPS aggregate strength.

Explanation of symbols

1 Reinforced concrete member 2 Reinforcing bar 11 Area where EPS is large 12 Area where EPS is small

Claims (6)

Reinforced concrete members subjected to bending stress, in which the mixing rate of the foamed resin fine aggregate near the neutral axis of the member is larger than the edge of the member. The reinforced concrete member according to claim 1, wherein the mixing rate of the foamed resin fine aggregate in the neutral shaft is maximized, and the mixing rate of the foamed resin fine aggregate is decreased at a constant rate toward the edge of the member. The reinforced concrete member according to claim 1 or 2, wherein the mixing ratio of the foamed fine resin aggregate is zero in the vicinity of the upper edge receiving the maximum compressive stress and the lower edge receiving the maximum tensile stress. The reinforced concrete member according to any one of claims 1 to 3, wherein the foamed resin is obtained by roughly pulverizing waste foamed polystyrene, reducing the volume by heating, and finely pulverizing the foamed resin. The reinforced concrete member according to any one of claims 1 to 4, wherein a volume mixing ratio of the foamed resin fine aggregate is 40% or less. The reinforced concrete member according to any one of claims 1 to 5, wherein the foamed resin fine aggregate has a particle size of 4.0 mm or less.

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