INSTALLATION OF PREFABRICATED CONCRETE AND CONCRETE STRUCTURES 9. Casting joints and seams

Threshing of joints should be performed after checking the correctness of installation of structures, acceptance of connections of elements in the joints and the implementation of anticorrosive coating of welded joints and damaged areas of the coating of embedded products.
The class of concrete and the grade of the mortar for the grouting of the joints and seams should be indicated in the project.
Concrete mixtures used for the grouting of joints must meet the requirements of GOST 7473-85.
For the preparation of concrete mixtures should be used quick-hardening Portland cement or Portland cement M400 and above. In order to intensify the hardening of the concrete mixture in the joints it is necessary to apply chemical additives - hardening accelerators. The largest grain size of coarse aggregate in the concrete mix should not exceed 1/3 of the smallest cross-section of the joint and 3/4 of the smallest clear distance between the reinforcement bars. To improve workability in the mixture plasticizing agents should be introduced in accordance with Section. 2
Formwork for the embedment of joints and seams, as a rule, should be inventory and meet the requirements of GOST 23478-79.
Immediately before embedment of the joints and seams it is necessary to: check the correctness and reliability of the installation of the formwork used for the monolithing; clean the joined surfaces from debris and dirt.
When monolithing joints, the compaction of concrete (mortar), its maintenance, control of the holding mode, as well as quality control should be performed in accordance with the requirements of Sec. 2
The strength of concrete or mortar at the joints at the time of stripping should be as specified in the project, and in the absence of such an indication, it should be at least 50% of the design compressive strength.
The actual strength of the laid concrete (solution) should be monitored by testing a series of samples made at the site of the monolithing. To test the strength, at least three samples should be made per group of joints concreted during this shift.
Tests of samples must be made according to GOST 10180-78 and GOST 5802-86.
Methods of preheating of joined surfaces and warming up of monolithic joints and seams, duration and temperature-humidity mode of curing concrete (mortar), methods of warming, terms and procedure for removing and loading structures, taking into account the peculiarities of work in winter conditions, as well as in hot and dry weather should be listed in the CPD.