Abstract: In recent years, a large number of buildings with different styles and different wall structures have been built in China by using new wall materials. Wall reform has developed to a new stage. Block building is a building with small and medium-sized blocks made of fly ash (or other industrial waste residue) and concrete as the main raw materials to replace ordinary clay bricks. The mechanical properties of masonry buildings are high compressive strength, high tensile strength, high bending strength and low shear strength. This paper analyzes the main points of masonry engineering from three aspects: the quality of masonry mortar, the quality of block and the common problems in masonry process.

Keywords: masonry analysis

1 quality of masonry mortar

The quality of masonry mortar undoubtedly has a great influence on masonry engineering. The poor workability and water retention of masonry mortar make it difficult to spread and squeeze mortar during masonry, which affects the bonding force between mortar and brick and reduces the compressive, tensile and shear strength of masonry. Or the strength of masonry mortar fluctuates greatly and the uniformity is poor.

Cause analysis of 1. 1

The quality of materials used is unqualified or the mixture ratio of mortar is wrong. The quality of cement directly affects the performance of mortar. Using cement with poor stability produced by small factories or cement caked by moisture during storage often leads to low strength grade of mortar. The large silt content of sand makes the mortar have high viscosity, large shrinkage, low strength and poor durability; When mixing mortar, the components are not measured, and the mixture ratio of mortar is inaccurate, which often makes its strength fluctuate greatly and most of it is low. From the analysis of building collapse accidents, the strength grade of building masonry mortar with collapse accidents is generally lower than the design requirements.

1.2 preventive measures

(1) Cement mortar is made of cement, and sampling test should be conducted before use, and it can only be used if it is qualified. It is forbidden to use waste cement.

② Different types of cement cannot be mixed. This is due to the different components of various cements, which often lead to material changes and strength reduction after mixed use, resulting in engineering accidents.

(3) The silt content of sand in mortar shall comply with the regulations.

(4) Strictly control the mixture ratio.

⑤ In order to improve the workability and water retention of mortar, lime putty is added as plasticizer. It is forbidden to use dehydrated, hardened, frozen and polluted lime putty.

⑥ Mortar in the ash tank must be used as it is mixed, and it is forbidden to continue to use untreated mortar the next day.

⑦ Mortar strength grade shall be randomly sampled at the site to make test blocks according to regulations, and the compressive test results of standard curing for 28D shall prevail.

Today mortar appropriate USES mechanical mixing. Mixing time should meet the specification requirements. Feeding is divided into two steps: first, add some sand, water and all lime putty; After the lime is dispersed by blade stirring and sand grinding, the remaining sand and all cement are put in.

2 mass

Build a wall with unqualified secondary bricks. The strength of masonry can not meet the design requirements, resulting in cracks in masonry and serious collapse accidents; When used in brick walls, mortar is not easy to spread, brick joints are not easy to be full, and the adhesion between dry bricks and mortar is poor, which makes the wall easy to seep, the masonry quality is poor and the strength does not meet the requirements.

2. 1 Cause analysis

Whether the strength of brick meets the design requirements is the basis to ensure the mechanical properties of masonry. If the wall is built with low-strength bricks, especially bricks with insufficient firepower when fired, the bearing capacity of bricks will be reduced and the design requirements will not be met. In addition, as a part of brick masonry construction technology, the wetting degree of brick has a great influence on the construction quality of brick masonry. The comparative test shows that proper moisture content can not only improve the bonding force between brick and masonry, but also improve the shear strength of masonry, maintain the normal growth of mortar strength and improve the compressive strength of masonry. The test results show that the shear strength of the wall built with dry bricks is 465,438 0.6% lower than that of the wall built with wet bricks.

2.2 Preventive measures

Bricks used for masonry can only be used for masonry after passing the sampling test, and unqualified bricks are prohibited from entering the site for use; Check the bricks that have entered the site, and reject the unqualified bricks; If there are sub-bricks with the amount of 1/2, which have been clamped in the wall, they must be removed; Before and during bricklaying, it is necessary to strengthen the process management of bricklaying, water by designated personnel and improve the methods and requirements of bricklaying.

3 common problems in the process of masonry

3. 1 masonry scheme error

Brick columns are built by core-cladding method, and there is no staggered joint between bricks. Vertical joint is a bottom-up joint, but the joint can't transfer shear force, which leads to the brick column can't become a whole. When the brick column bears a large eccentric load, it produces local compression and tension, which makes the core column unstable and damaged under the action of external force. The wrong method was used in masonry. According to the fact, the core wall adopts the way of five-in-one or even more than twenty-in-one, and the bricks are not connected, so they can't transfer shear force to each other and destroy it prematurely.

3. Cause analysis of1.1

Managers have insufficient understanding of the importance of masonry quality and poor management. The bricklayer has not been trained, is not familiar with the operating procedures, and has insufficient basic skills in bricklaying.

3. 1.2 preventive measures

In order to ensure the integrity of brick masonry, the construction should be carried out in strict accordance with the specifications. The specification requires that brick masonry should be staggered up and down, with internal and external overlapping. Solid brick masonry can adopt straight-line, plum blossom D-shaped or three-in-one D-shaped masonry, and it is especially pointed out that "brick columns shall not be built with cores". Foreman should strengthen management, carefully coordinate interface construction, and clarify responsibilities.

3.2 vertical and horizontal wall if not firm

Masonry corners and junctions are generally straight, but Rachel steel bars are not placed as required; Some projects don't meet the requirements, such as leaving an oblique if only under the wall 1cm, and leaving a straight if on the upper part; In other projects, the first floor of the external wall is almost built to the flat mouth, and the joints of the internal and external walls are all kept straight, and then the internal wall is built; If the joints are sloppy, there is almost no mortar at some joints. All these have seriously affected the integrity and seismic capacity of the house.

3.2. 1 Cause analysis

The site management is chaotic, the bricklayer's arrangement is improper, and the coordination at the interface is not in place; The bricklayer's basic quality is low, and he is not familiar with the operating procedures or illegal operations.

preventive measure

In the construction of brick-concrete building, the firmness of the corner and junction of masonry is the key to ensure the integrity of the building. The specification requires that the corner and junction of brick masonry should be laid at the same time, and it is strictly forbidden to separate the internal and external walls without reliable measures. For temporary breaks that cannot be laid at the same time but must be preserved, oblique gaps should be made. If it is really difficult to leave an oblique corner, you can also leave a straight corner, but it must be convex, and Rachel bars should be added at intervals of not more than 500 mm along the wall height, and the embedded length of each side should not be less than 500 mm. The connection part of the temporary discontinuity in brick masonry construction is itself a weak link, which must be cleaned, wet and filled with mortar.

3.3 mortar joint is not full

The mortar between blocks is not full, and the tensile strength and shear strength of masonry at the empty joints are reduced, which easily leads to cracks in masonry under load and affects its strength. In addition, rainwater will penetrate into cracks, and the sound insulation, heat insulation and heat preservation performance are poor, which will affect the normal use of buildings.

3.3. 1 Cause analysis

Due to the poor workability of cement mortar, the mortar is not easy to squeeze during masonry. After the operator leveled and scraped the mortar with a shovel or tile knife, the bottom ash produced holes, the mortar layer was not full, and the bond between brick and mortar layer was poor. Sometimes because the paving time is too long, the masonry speed can't keep up, and the moisture in the mortar is absorbed by the bottom brick, so that the brick layer on the masonry can't be bonded with the mortar; Used for brick wall construction, early dehydration of mortar, reducing strength. The crumbs on the surface of dry brick play an isolation role, which weakens the bond between brick and mortar layer. The operator's basic skills are not solid, and the slurry is not squeezed enough when laying bricks, resulting in empty joints or blind joints.

preventive measure

The fullness of mortar in horizontal mortar joint has a great influence on the strength and integrity of masonry, and vertical mortar joint has a significant influence on the shear strength of masonry. The specification requires that the plumpness of horizontal mortar joint shall not be less than 80%; If the vertical mortar joint is not full, the shear strength of masonry will be reduced by 40%-50%. Specific measures are as follows:

① Improving the workability of mortar is the key to ensure full mortar joint and improve bond strength.

(2) To improve the masonry method, we should popularize the "trinity bricklaying method", also known as the squeezing method, that is, "one knife ash, one brick, one squeezing and kneading".

(3) It is strictly forbidden to be used in brick walls. For the earthquake area fortified with design intensity of nine degrees, it is not suitable for masonry when bricks cannot be poured in severe winter.

3.4 Quality problems of clean water wall surface

The horizontal mortar joint of drywall is not straight, and the wall is uneven; As for the fair-faced wall, the vertical joints of T-bricks are skewed and uneven in width, and the T-bricks are not centered (the T-bricks are not centered on the lower bricks), and the vertical joints between the window sill and the window wall are displaced, resulting in the so-called "spiral wall", that is, when building a high-rise wall, the elevation of the same floor is one skin brick thick and cannot overlap.

3.4. 1 Cause analysis

Loose management, fear of trouble, no skin pole when building walls, making horizontal joints out of control, high error; Improper application of broken bricks, some will concentrate broken bricks in a certain part, resulting in continuous joints.

preventive measure

In strict accordance with the requirements of construction technology. Before building a wall, set skin poles at the four corners of the building and a certain distance along the length direction, and indicate the specifications of bricks and blocks and the thickness of mortar joint on the skin poles according to the design requirements, and indicate the change of vertical structure, and the thickness of mortar joint should be controlled between 8- 12mm; Broken bricks must be scattered with the whole brick in time, and laid on the inner wall and the parts with less stress. They shall not be laid on the wall between windows or on the battlements with greater stress, nor shall they be laid into seams with more than four skins.

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