What Are Masonry Joints?

Wall cracks are very common in brick-concrete structures. The main reasons for the cracks are masonry stubble, poor stubble treatment quality, and under the influence of environmental factors, the cracks continue to expand due to the poor quality of the masonry , These situations will have great hidden dangers in the use of engineering safety and functions

The wall masonry construction is an indispensable step in the construction of a building project, which has a separation and load bearing

1.Set the wall tie bar

The tie bar can be set to the frame column, the shear wall and the brick partition wall. Compared with the wall length, the tie bar length should be more than 20%, that is, 700 mm or more. Embedding of tendons can be carried out in a rear-mounted manner, requiring unloading construction and stacking on the working surface to provide convenience for masonry and use, followed by tensile strength test. It is required to carry out the tie bar construction of the frame column infill wall strictly in accordance with the brick modulus regulations, and there must be no bending problems or pressing into the brick joint.

2. Construction line

According to the control axis of the floor, the wall axis of each floor and the position line of the door and window openings are measured and released in advance. After the completion of the construction laying operation, ensure that its quality meets the construction requirements before the brickwork can be performed.

3. Grass-roots processing

Before the construction of masonry bricks, the base of the wall must be thoroughly cleaned, such as clearing the floating ash layer on the floor, so as to moisten the base.

4. Construction column setting

Compared with the floor height, if the wall length is more than twice, the reinforced concrete structural column can be set to the middle position of the wall length; if the wall height is more than 4m, the reinforced concrete ring beam can be set to the middle of the wall and the top of doors and windows. At the same time, the longitudinal reinforcement of the ring beam should be anchored in the frame column. If the shear wall is not stored around the elevator shaft, the construction column can be set according to the design regulations. According to the specific conditions of the project, the reinforced concrete structural columns in the masonry need to be built first, and then the pouring construction is carried out. At the same time, the wall tie bar reinforcement can be set.

5. Masonry construction

In the early stage of masonry walls, the foundation walls and floor positions need to be thoroughly cleaned and moisturized. According to the construction regulations, the building method shall be reasonably determined to facilitate the construction. When configuring the mortar, the error should be controlled reasonably, such as the cement is controlled between -2% and + 2%,

Sand and admixture should be controlled between -5% and + 5%. The mechanical stirring construction needs to be controlled for more than 1.5 minutes. After mixing for 3 to 4 hours, the mixed cement and cement mixed mortar must be used in time. It is forbidden to use the mortar the next day. During the construction of the hollow brick wall, a reasonable method of masonry should be selected, the upper and lower joints should be staggered, and the joints should be bitten and erected. Usually, the hollow bricks with severe corners should not be selected. And control the horizontal gray seam between 8 and 12mm, and select mortar to fill the vertical seam sufficiently. In short walls, brick columns, etc., solid bricks can be selected for hollow brick wall masonry. When beams and floor slabs are located, hollow bricks can also be compacted and slanted with solid bricks and filled with mortar. In addition, solid bricks can also be used on the two sides of the hollow brick wall door and window frame, and the length must be controlled above 24cm.

According to the design regulations, hollow brick walls can be provided with structural columns, ring beams, cross beams, etc. The corners and transfer positions can be built together, and there must be no straight retaining. Compared with the height, the horizontal projection length of the oblique concrete should be controlled above 70%, and its height should be controlled below 1.8m. During the masonry construction of the pull-through line, the wall must be vertical and flat, and no problems such as smashing bricks to repair the wall must occur. The cable is led out of the wall at the end of the tie bar. According to the construction drawing, the cantilever beam and the infill wall under the outer beam and the infill wall under the small stiffness beam can be flexibly connected. For the masonry construction to the bottom of the floor, it is necessary to select the inclined block to be stable and install the horizontal tie bars. When the masonry construction is required to be carried out on the floor of the building, the corresponding gaps should be reserved first. After 7 days from the completion of the masonry construction of the infill wall, the site can be repaired and compacted; if the masonry is not carried out on the floor Concrete jacking setting is required, and 60mm is its jacking thickness.

6. Retention and filling of construction holes

The project can be divided into 1-6 # buildings, the construction holes can be set to the deformation joint positions of 2, 3, and 6 # buildings, and the reinforced concrete lintel is set to the upper part, and 250 is the length of each side lintel support. On both sides of the entrance of the cave should be left straight retaining, generally the convex form is the main form, and the tie knots are set. It is required to set a reinforcing bar (diameter 6.5mm) when the thickness of the wall is 120mm, and set the distance along the wall height, which should be controlled within 500mm, and the embedded length calculation based on the wall retaining position, which needs to be controlled above 500mm, 90 degrees is Hook of steel bar tail. When filling the temporary opening, the debris on the wall must be cleaned up, such as mortar, and the moisture retention work must be done. Compared with other parts, the strength level of the mortar selected for the construction cave needs to be higher. Generally, the opening construction is carried out in an inclined way To ensure that the opening is tightly sealed. ^[1]

The main causes of cracks in masonry include the following: First, the deformation caused by temperature. Due to the different temperature, the deformation of each material and structure is inconsistent, and they have a relatively large binding force with each other, and the temperature difference is too large; The second is the uneven settlement of the foundation. For example, in a brick-concrete structure with a large length and a high height, when the foundation at both ends is smaller than the middle foundation, the splay crack is easy to occur, but when it is larger than the middle, the inverted splay crack is easy to occur; The last is the unqualified material quality, unqualified cement quality, pyrite sulphur content exceeding standards, etc. will cause masonry cracks. ^[2]

1.Masonry and plastering material control

The block is made of concrete. Unlike clay bricks, which need to be sintered, the shrinkage value of small blocks is relatively large. After 28 days of natural curing, the shrinkage is not complete. The wall will still shrink and deform after plastering. Shrinkage stress is generated, which causes irregular hollow drums to crack. Therefore, the quality of materials must be strictly controlled, and the materials must be controlled according to the following requirements. First of all, the incoming materials should be inspected and rechecked by sampling, and the block certificate and quality certification documents should be checked. Cracked, damaged and less than 28 days old blocks are strictly prohibited. Secondly, the blocks entering the site should be covered to avoid rain, and the top layer should be removed from the wet wall of the already built wall before continuing to build. Finally, the mortar used in masonry and plastering must meet the strength and mix ratio required by the design. The cement used must be of the same brand and the same designation. It is forbidden to mix different brands of cement, prohibit the use of expired or damp cement, and prohibit the use of less than 32.5MPa of cement, gypsum is not less than 15d, dehydrated lime paste is prohibited to replace the mature lime, plastering and masonry mortar should be used with mixing, do not re-stir the set mortar before reuse.

2. Crack control in masonry construction

When building a wall, the main specifications must be used (390mmx190mmx190mm), supplemented by auxiliary blocks, adhere to the principle of "on holes, staggered seams, and reverse masonry". Staggered by 1/2 the length of the main specification block. The corner of the wall and the junction of the internal and external walls should be built at the same time and overlap each other. When there is a break in time, stubble should be built, and straight stubble is strictly prohibited. The length of the stubble should be equal to the height of the stubble. The vertical joint mortar fullness control is relatively weak, so the ribbed grooved end of the block should be laid flat during masonry. Cover the mortar first, squeeze it, and use a brick knife to cut and vibrate. It is necessary to grout the joints that are not full. The thickness of the gray joints should be controlled within 8-12mm, and the horizontal gray joints of the mortar fullness must reach 90%, and the vertical joints must reach 80%. C20 concrete can be poured into the block holes on both sides of the door and window openings of the house to connect the door and window with the wall. Holes, pipes, trenches, and embedded parts required by design or construction must be pre-buried or reserved when the wall is built, and no holes or gouges must be made in the wall. Collision of the masonry wall is strictly prohibited, and the masonry wall is well protected.

3. Plastering crack control

The plastering of the wall should not be started until the wall has been stabilized for at least a certain period of time (at least 30 days). Plastering should not be performed immediately after the wall has been laid. The plastering of the block wall should be moistened with water 2 to 3 days in advance. The weather is particularly hot and dry and can be watered 1 day in advance. However, the bottom plastering must be carried out when there is no water stain on the wall surface. Thoroughly remove loose masonry mortar, dust, and stains on the wall before plastering. If the surface of the base layer is too smooth, the plaster will not adhere well, so use a cement slurry to brush the hair before plastering. ^[2]