ANNEX 2
TO CONTRACT AGREEMENT No. 13/06/2023 FROM 13.06.2023
ATTITUDE
on the organization of conditions during the performance of works on the installation of concrete pavement, priority measures for its care and the algorithm of actions when cracks are detected
This Guide was developed in accordance with DSTU B V.2.7-176:2008 "Building materials. Concrete mixtures and concrete. General technical conditions", DSTU B V.2.6-2:2009 "Concrete and reinforced concrete products. General technical conditions", DSTU B V.2.6-156:2010 "Construction of buildings and structures. Concrete and reinforced concrete structures made of heavy concrete. Design rules"
This Instruction is an integral part of the Contract. By signing the Agreement, the Customer confirmed that he is familiar with all the terms of the Guidelines, fully understands and agrees with them.
TermsIn order to obtain an ideal surface without cracks or to minimize them, it is necessary to ensure the proper temperature and humidity regime of concrete hardening in the first 3-5 days in the summer period and 5-7 days in the winter period (or until the concrete strength of the structure is at least 10 MPa). It is necessary to protect the structure from cracking due to temperature deformations both at the stage of designing the composition of the concrete mixture, using mineral and chemical additives that reduce the intensity of exothermic reactions in concrete, and at the stage of concreting works, namely by ensuring the care of the structure in such a way that the speed cooling of the concrete did not exceed 1-5°С/day (depending on the massiveness of the structures), and the difference between the surface of the concrete and the ambient air did not exceed 18°С. This can be achieved by closing the perimeter of the premises around the clock.In the initial period of concrete hardening, it is necessary to maintain a favorable temperature and humidity regime, which is necessary for the normal course of concrete hardening and the timely completion of the processes of expansion and compaction of the concrete mixture.The technological care of concrete aims to:- ensure optimal temperature and humidity conditions in fresh concrete;- protect freshly laid concrete, after laying, from exposure to the sun, wind, rain, snow;- limit shrinkage of concrete, which is the cause of sudden drying of the surface;- reduce the temperature difference on the surface of the concrete and inside it (as there is a danger of cracks in the concrete due to temperature differences);- prevent freezing of water in fresh concrete and ensure the necessary course of hydration processes at low air temperatures.1.4. At the same time, periodic watering of open surfaces of concrete and reinforced concrete structures with water is not allowed.
1.5. All cracks are divided into structural and natural (intrinsic, non-structural) according to the reasons for their appearance.
Structural cracks are those formed in concrete as a result of the applied force, constant static load or other external influences that exceeded the strength of concrete and caused its destruction.
According to the chronology of formation and the specifics of manifestation, natural cracks can be classified depending on the processes that caused their appearance into the following:
Shrinkage cracks caused by plastic deformations of concrete (plastic shrinkage and/or subsidence) usually appear within the first 10-30 minutes. up to 6-12 hours of time; shrinkage cracks are characteristic of the summer season, and their manifestation depends on the care of concrete.Thermal cracks caused by early thermal shrinkage, which are formed between the first day of concreting and 2 weeks; the manifestation of thermal cracks is characteristic of densely reinforced and massive structures.Structural cracks formed as a result of the hardening and drying of concrete after several weeks or even months.1.6. Care measures for the concrete coating do not directly depend on the concrete compressive strength class. More important is the factor of seasonality (winter, summer) of work performance.
2. Care methods
2.1 Concrete must be protected from moisture loss at the early stage of hardening. This can be done in two ways:
- method of wet care (in the case of an area of up to 100 square meters of the open surface of the concrete structure);
- application of external protection on the concrete surface (membrane former).
3. Care of concrete in the summer - wet care method
3.1. The main task of wet maintenance is to ensure contact of the concrete surface with water and protection against drying shrinkage.
A) The reason for the plastic shrinkage of the concrete mixture is the evaporation of water from the surface of the concrete mixture or its absorption by the surrounding layers of dry concrete, formwork, and soil.
B) The reason for the shrinkage of hardening concrete is the rapid loss of water by the concrete in conditions of low humidity, hot weather, and strong wind.
3.2. You can protect concrete from drying shrinkage in several ways:- spraying the membrane former on the concrete surface;- protection of concrete with burlap (geotextile), which must be watered (in the case of concreting in the open air).
3.3. The temperature of the concrete mixture when concreting structures with a surface modulus of more than 3 should not exceed 30-35°С, and for massive structures with a surface modulus of less than 3-20°С.
Surface modulus is the ratio of the product's surface area to its volume.
3.4. If cracks appear on the surface of the laid concrete due to plastic shrinkage, its repeated surface vibration is allowed no later than 0.5-1 hour after the end of its laying.
3.5. Care of freshly laid concrete (covering and watering) should be started immediately after the laying of the concrete mixture and its processing and carried out until reaching 70% of the design strength, and with appropriate justification - 50%.
3.6. To protect surfaces that are under the open sky, concrete should be covered with rolled material with moistening and their coating with film-forming (membrane-forming) solutions.
3.7. It is forbidden to pour cold water directly on the concrete during the sunny hours of the day.
4. Minimum wet care time for concrete
       4.1. Application of external protection on the surface of concrete
External protection on the surface of concrete is aimed at applying a coating that protects against heat and moisture loss. Water is not used in this care method.
This method includes:
- covering the concrete with dense oilcloth or glued fabric (in cold weather or moderate temperatures). In the summer, it is better to use a white film;
- use of tents - protection from strong wind, snow, rain - protects freshly laid concrete from drying out and overheating, prevents surface destruction by rain;
- application of chemical film-forming solutions to protect the surface from drying out.
5. Responsibility.
5.1. The contractor is responsible for:
- the right choice of concrete care method depending on the conditions;
- timely notification of the Customer about the need to include the necessary materials in the project estimate or his independent ordering of the necessary materials for the appropriate care of concrete.
5.2. The customer is responsible for:
- unsatisfactory result of the work performed, if the Customer, despite a timely warning from the Contractor, does not change the instructions on how to care for concrete or does not eliminate other circumstances that threaten the quality or suitability of the concrete coating;
- consideration in the project estimate of materials that form a moisture-proof, non-vapor-proof film, or works to cover the concrete surface with a polyethylene film to ensure maximum grafting and tightness;
- ensuring the proper temperature and humidity regime of concrete hardening by closing the perimeter of the room around the clock to prevent drafts and sunlight, maintaining a constant temperature in the room;
- provision of electricity supply, water supply of sufficient capacity, ventilation at the facility.
6. Cracks and methods of their elimination

6.1. When cracks are formed, the first stage will be to establish their geometric parameters and determine their localization, based on which an assessment of their possible impact on the technical and operational characteristics of the structure is made.

6.2. According to the requirements of DSTU V.2.6-156:2010 "Constructions of buildings and structures. Concrete and reinforced concrete structures made of heavy concrete. Design rules" clause 5.3, for structures with environmental exposure classes ХО and ХС1, according to DSTU B V.2.7- 176:2008 "Building materials. Concrete mixtures and concrete. General technical conditions" clause 4.1., the width of the cracks does not affect the durability of the concrete structure, therefore, the presence of shrinkage cracks is not considered a defect.

6.3. According to DSTU B V.2.6-156:2010 "Concrete and reinforced concrete structures from heavy concrete. Design rules", clause 5.3.1 "The formation of cracks is normal for reinforced concrete structures that are subjected to bending, shearing, twisting or stretching caused by direct loading or limitation of applied deformations. The formation of cracks should be limited to a level at which they do not affect the proper functioning of the structure or they are acceptable."

6.4. The recommended values of wmax for the relevant impact classes are given in table 5.1 of DSTU B V.2.6-156:2010 "Concrete and reinforced concrete structures made of heavy concrete. Design rules". If, according to the results of the instrumental examination, the cracks exceed the specified limits, are classified as structurally dangerous, or the customer has reservations about the very fact of their presence, it is necessary to carry out repeated calculations of reinforced concrete products, taking into account the following conditions (according to DBN V.2.6-98:2009 "Concrete and reinforced concrete constructions. Basic provisions of design"). For structures operated in conditions protected from climatic influences, the maximum permissible crack opening width should not exceed 0.5 mm; for structures exposed to climatic influences - 0.4 mm; for structures operated in aggressive environments - 0.3 mm; for structures with increased sensitivity to corrosion - 0.2 mm.

6.5. If, as a result of studying and researching cracks, it was established that they can affect the durability of the structure, then it is necessary to carry out repair work to eliminate defects. Repair works depend on the assessment of the risks caused by the formation of cracks, and according to the degree of complexity, they are divided into several types:

6.5.1. Surface cracks with a width of up to 0.5 mm and a depth that does not exceed the thickness of the protective layer of concrete above the reinforcement, which represent only an aesthetic defect, are masked by carrying out cosmetic repairs using a fine-fraction cement repair mixture applied with an elastic spatula. In the future, the surface can be polished.

6.5.2. Surface cracks with a width of up to 0.5 mm and a depth exceeding the thickness of the protective layer of concrete above the reinforcement, during the operation of the structure without secondary protection (treatment) under conditions of exposure to the surrounding natural environment (rainfall, temperature drops, etc.), as well as concrete structures , which have higher durability requirements, need to be repaired with cement or polymer repair mixtures, which can be carried out either by the injection method or by filling defective areas (according to the recommendations of the manufacturer of repair mixtures).

6.5.3. Surface cracks with a width of more than 0.5 mm and a depth exceeding the thickness of the protective layer of concrete above the reinforcement need to be repaired using repair mixtures, the maximum fraction and strength of which is selected depending on the geometric parameters of the damage. In some cases, repair work involves "stitching" of cracks and their subsequent repair, to ensure higher reliability and efficiency of the work carried out.

6.5.4. Through cracks, regardless of the geometric parameters, are first treated with polymer mixtures to protect the steel reinforcement from corrosion, and then putty.

6.6. Algorithm of actions upon detection of cracks

6.7. Based on the results of the work performed, an Act is drawn up and (if necessary) recommendations are made for the elimination of cracks and a work plan is approved.