裂缝对不同龄期小型空心砌块的影响分析

The 12th International Symposium on Structural Engineering

THE IMPACT OF CRACKS ON DIFFERENT AGE OF CONCRETE

SMALL-SIZED HOLLOW BLOCK MASONRY

Yin Wang, Zhijian Shi, Yadi Hu

College of Urban and Rural Construction, Agricultural University of Hebei，Baoding 071000,P.R. China

Abstract: In the latter part of concrete small-sized hollow block masonry cracks after using many reasons, including the design factors that are not in place, the material factors, construction factors, climate, natural conditions, factors, etc., in which the age of c concrete small-sized hollow block length of cracks in the masonry of the impact is different. Cracks in the masonry structure will cause adverse effects, affecting the use of construction and durability, this paper field test, to identify non-instars of concrete small-sized hollow block masonry cracks on impact. To reduce or prevent age of concrete hollow block the effects of crack, to strictly control the construction of block wall on the age, age as long as possible, especially in areas influenced by temperature, such as wall, the top wall, should pay attention to blocks of age, in a possible, concrete hollow block age should be greater than 42 days, the best age to block more than 56 days is better.

Keywords: Concrete small-sized hollow block, crack, age of concrete block

1 INTRODUCTION

Cracks in the late after use of the concrete small-sized hollow block masonry for many reasons, of which the design is not in place, material factors, construction factors, climate, natural conditions, factors, including age concrete small hollow block of the length of the masonry cracks .

Block forming the conservation, the shrinkage rate of 0.35~0.50mm/m than clay brick wall contraction .Shrinkage will produce considerable stress,when the masonry mortar strength, cohesion, and certain areas of mortar joint is not full, the wall there will be shrinkage cracks . In particular, the rush period, the conservation of wet block on the wall, natural shrinkage, wet block mortar joint around the hairline cracks. “Concrete small-sized hollow block building technical regulations”JGJ/T14-2004, “Technical specification, masonry structure constructed detail”02G01-2,to prevent cracks also made provisions effectively prevent and reduce cracks played a role.

2 THE AGE OF THE CONCRETE SMALL HOLLOW BLOCK CRACKS

In order to test the age of concrete small hollow block masonry with manufacturers consultation, not the age of the block in the block manufacturer to cover production houses, masonry masonry management space plane shown in Figure 1 :

Production management space is a single layer, housing bay 3300mm deep into 4200mm, the height is 3200mm .

In-situ concrete roof, concrete strength C20, 60 thick polystyrene board roof insulation, the outside corner and three core columns, T- walls have four core columns, core pillars anchored into the ground beam and floor, there is no ring beam, the basis of strip foundation, each room has a 900mm door, leaving the stack 200mm, 1500mm windows a center set, the external walls of face brick, interior wall plaster walls, brush the white latex paint . Roof hipped color steel roof .

In order to test a unified environment, the block is so arranged that : used for external walls is the age of 84 days of the block, ②③ axis transverse wall the age of 21 days of the block, ④, ⑤The axis of the transverse wall with age for the 28-day block, ⑥, ⑦ axis cross- wall with the age of 42 days block, ⑧, ⑨ axis of the cross wall of the age of 56 days of block . All the blocks using the MU10, masonry mortar to adopt Mb5 mixed mortar .

Housing built after a year and a half, the cracks generated by the housing survey,

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different wall vertical crack width as shown in

Table 1

Figure 1. Production management space level map Table 1. Crosswall cracks of different width (mm)

crosswall Crosswall of ①⑩axis

Crosswall of ②③

axis

Crosswall of ④⑤axis Crosswall of ⑥⑦axis

Crosswall

of ⑧⑨axis

width of crack

vague 0.5~0.80.1~0.2

vague invisible

It can be seen from Table 1, concrete small-sized hollow block masonry wall, the size of the cracks is indeed the age of the block length of cracks ② The ⑨ axis intermediate transverse wall can be seen, the age the longer the period, the smaller the cracks, age over 28 days, produce a very small cracks, when the age reaches 42 days, cracks were visible when the age reaches 56 days, no cracks apparent .

Table 1 shows the concrete small hollow block production later in the process of formation strength, concrete block may also occur shrinkage deformation, if the short block of the age of the block has not yet fully shrinkage deformation masonry masonry masonry masonry in a row from the subsequent shrinkage deformation of cracks, the age of the shorter block performance is more obvious, the longer the age of block masonry masonry cracks more smaller.

① and ⑩ shaft external wall cracks are barely visible, and ⑥ ⑦ axis transverse wall interior wall similar reason, ①, the ⑩ shaft external wall is not just the cracks and to shrinkage deformation of the block, due to the external walls insulation measures, cracks in the wall and indoor and outdoor temperature difference is related to both work together to make wall cracks

3 IMPROVEMENTS

Not the age of the concrete small hollow block cracks is different, the smaller the age of the longer block masonry cracks in the wall, on the contrary, the greater the cracks . Therefore, during the construction of small concrete hollow block masonry, approach the age of the concrete small hollow block of control.

In order to guarantee the quality of the concrete small hollow block masonry, test analysis comparison of several measures :

(1) Strict control of the small hollow concrete block, age, approach the block must have a product certificate .

(2) Age-site construction of concrete small hollow block should be greater than 42 days, and

the best selection of concrete small hollow block age greater than 56 days .

(3) Generally small hollow concrete block factory age of 28 days, during construction preparation conditions of the site license, the block should be completed before ordering, early approach, moisture, rain at the scene to take measures to ensure that the block on wall masonry of age more than 42 days is appropriate .

(4) Such as facades, and the top wall masonry affected by temperature of the wall, try to use the age of greater than 56 days of the block, to ensure the quality of the masonry .

(5) Possible after the completion of the main masonry, post-renovation try to stagger the time interval, so that the concrete small hollow block as far as possible complete the shrinkage deformation .

4 RECOMMENDATIONS

To reduce or prevent the cracks of different ages of concrete small hollow block, to strictly control the block wall construction on age, age

as long as possible, especially by the temperature greater impact on areas such as external walls, the top-level wall, should be noted that the block of the age of possible concrete small hollow block age should be greater than 42 days, it is best used to block better with age greater than 56 days .

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Gao Xiaoping, the Jingui real, Sanchi Cheung .02 G01, masonry structure

construction detail. Beijing, China Planning

Press, 2003 .

The Sun cyanide Ping, Tangdai, new, Yan Xi .JGJ/T14-2004 Concrete Small Hollow

Brickwork Construction Technical Regulations. Beijing, China Building Industry

Press, 2004 .

Zhang Guan Fu, Yong-Feng Liu . (2000). Of the crack of the Concrete Small Hollow Block

Construction Design. New wall Materials and

Construction, 1:35-37.

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