Construction time in winter: According to the "Construction Rules for Winter Construction of Construction Projects" (JGJ / T104-2011), the average daily temperature of the day is stable below 5 ° C for 5 consecutive days, which is the start date of the winter application; the daily average temperature is stable and higher than 5 ° C is the end date of winter application. According to Beijing's many years of meteorological data statistics, generally from November 15th to March 15th of the following year is the winter construction phase of construction projects.
According to the characteristics of the weather conditions in Beijing in the past years, we divided the winter construction into two phases: early winter (November 15-December 15) and severe winter (December 15-February 15 of the following year). (Below -10 ℃ as the standard), according to the temperature of each period, reasonable raw materials and additives will be selected to ensure product quality. However, in principle, it is recommended that the construction unit stop the mortar project construction during the severe winter period.
The company's technical quality department should hold a special meeting before the winter application to specifically arrange the winter application preparations, and implement the responsibility to the relevant departments and specific responsible persons. During the winter application, the quality controller is responsible for grasping the changes in the weather. When the weather changes suddenly, the relevant departments should be notified in time to take necessary protective measures.
2. Technical requirements for raw materials
In order to ensure the smooth construction of the winter season, the material department should cooperate with the technical and quality department to start the storage of various raw materials two months in advance. Before the winter application arrives, actively find the source and evaluate the suppliers' winter application period. Production and supply capabilities, and sampling of suitable sources, the technical quality department should perform the test work on the samples as promptly and comprehensively as possible, and ensure the authenticity and integrity of the test data. The most important of these is sand, which should have sufficient reserves to ensure that sand with lower moisture content is used as much as possible during winter application.
2.1 Cement: Use low-alkali ordinary portland cement, and the strength grade should be P.O42.5.
2.2 Antifreeze: Select low-alkali and chlorine-free early-strength antifreeze, and the samples shall be inspected in accordance with the requirements of JC / T2031-2010 cement mortar antifreeze standard; in accordance with the provisions of the GB18588-2001 limit of ammonia release in admixtures.
2.3 Sand: Store the medium-quality sand in Zone II in advance, and control the fineness modulus between 2.3 and 2.8. During the winter feeding, strictly control the water content to be no more than 5%, and there must be no debris such as ice, snow, and frozen blocks. Requirements, classified storage of various types of sand.
2.4 Additives: According to the requirements of mortar quality, various types of additives that meet the requirements of winter construction are preferred.
3．Preparation and adjustment of mix ratio
3.1 Two months before winter application, the laboratory should test the antifreeze performance of the admixture, and on this basis, carry out the trial mixing and trial mixing of the dry powder mortar. According to the relevant provisions of dry powder mortar such as "Design Rules for Masonry Mortar Mixing Proportion" and "Technical Specification for Plastering Mortar", the winter application mix ratios of various dry powder mortars are finally selected through calculation and trial adjustment. All trial work should be completed before October 25, and submitted to the Chief Engineer for approval before November 5
3.2 The raw materials are relatively tight during the winter application. The properties of various materials, especially the properties of some additives, may be significantly different from those at normal temperature. The laboratory should try to select multiple materials for testing. According to the test results of the materials, Make a trial mix and reserve more mortar mix ratios of the same type and different material types in order to meet the various requirements during winter application as much as possible.
3.3 During the winter construction period, the Technical Quality Department should timely track the development of various technical indicators after the construction of various dry mortars, especially the loss of compressive strength and tensile bond strength of the mortar at low temperatures, and shall follow the tracking conditions. The mix ratio is adjusted appropriately.
4．Essentials of Quality Control
4.1 Before entering winter construction, the chief engineer organizes the company's relevant production and technical personnel, including testers, quality controllers, production line operators, material workers, drying line operators, repairers, etc., in accordance with the "Construction Regulations for Winter Engineering Construction" Relevant standards and specifications, strict training, grasp the specific technical requirements of winter construction, understand their respective job responsibilities, and better control production technology.
4.2 For important engineering and structural parts during the winter construction period, the chief engineer shall organize relevant personnel to compile a Quality Plan, and supervise the entire process of verification and implementation, and retain the records required to provide evidence for the realization process and the product to meet the requirements.
4.3 The test laboratory shall be responsible for the testing of various mortar test blocks, and analyze the situation with reference to the test configuration, and adjust the mix ratio if necessary. For important contracts, the Technical Quality Department shall cooperate with the operating department to conduct quality return visits to the construction site and do a good job of technical service.
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