The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.
 see figure 1 , the present invention provides a kind of technical scheme: a kind of construction technology of machine-made sand fair-faced concrete, the concrete steps of the construction technology of this machine-made sand clear-water concrete are as follows:
 S1: Install the formwork on the platform in strict accordance with the formwork assembly drawing, and pay attention to the accuracy between adjacent formworks to ensure that the shape and size of the engineering components meet the design requirements. Before the formwork is installed, the surface of the formwork needs to be cleaned and brushed with a release agent , and combined with the shape of the poured components, the formwork part that does not have universality is independently divided into a flow section. According to the principle of equal configuration of formwork in each flow section, it is reasonably divided so that the common parts of the formwork can be used in turnover and reduce formwork. input;
 S2: After positioning the steel bars accurately in the formwork, adopt the method of segmental lap joint at the main bars, and connect the main bars and auxiliary bars with wire tie;
 S3: After mixing Portland cement and machine-made sand, add mixing water to stir in the mixer, add mineral admixtures and admixtures, and continue stirring to form machine-made sand clear-water concrete mixture. The mixing water is colorless and tasteless domestic water, the mineral admixture is Class II fly ash, and the admixture is a water-reducing agent with high water-reducing properties;
 S4: After transporting the machine-made sand fair-faced concrete mixture to the site, first pour 30-50mm thick de-stoned cement mortar of the same machine-made sand fair-faced concrete and the same strength level on the formwork walls and column roots, and then pour the machine-made sand fair-faced concrete. Among them, the free cutting height of the machine-made sand fair-faced concrete is controlled within 2m, and if it exceeds 2m, it will be poured with string tubes. Before the concrete is poured, the inside of the formwork should be cleaned first, and then moistened with water after cleaning;
 S5: When the thickness of the pouring wall is greater than or equal to 50cm, use a vibrating rod to vibrate and compact the interior of the concrete. Vibration uses an inserted vibrating rod. It sinks again until no air bubbles overflow, and the extraction speed of the vibrating rod is 75mm/s to avoid segregation due to over-vibration. During the vibrating process, the distance between the vibrating rod and the surface of the machine-made sand fair-faced concrete should be kept not less than 50mm;
 S6: After the machine-made sand clear-faced concrete is solidified in the formwork, the machine-made sand clear-faced concrete project is demolished, and the surface of the machine-made sand clear-faced concrete is wrapped with a plastic film for moisturizing and curing.
 In the present invention, clear-faced concrete, materials and construction techniques should be kept consistent, and measures such as anti-cracking, anti-seepage, anti-pollution and airtightness must be taken, and the measures must not affect the effect of concrete finishes. The fair-faced concrete project should proceed to the next process after the quality acceptance of the previous construction process.
 1. Raw material requirements:
 (1) There should be sufficient storage capacity, and the color and technical parameters of the raw materials should be consistent;
 (2) Portland cement and ordinary Portland cement with a strength grade of not less than 42.5 should be selected. The cement of the same project should be from the same manufacturer, the same variety, and the same strength grade;
 (3) Coarse aggregate should be of continuous material grade, the color should be uniform, the surface should be clean, and it should meet the requirements of Table 1;
 Table 1 Coarse aggregate quality requirements
 (4) Machine-made sand fine aggregate, which should meet the requirements in Table 2;
 Table 2 Fine aggregate quality requirements
 Concrete Strength Grade ≥C50 ＜C50 Mud content (by mass, %) ≤2 ≤3 Mud content (by mass, %) ≤0.5 ≤1
 (5) The admixture used in the same project should come from the same manufacturer and the same specification and model, and Class I fly ash should be selected.
 In the mix design of fair-faced concrete, the mix design of clear-water concrete should comply with the current national standards "Construction Quality Acceptance Code for Concrete Structure Engineering" GB50204 and "Ordinary Concrete Mix Ratio Design Regulations" JGJ55, and should also meet the following requirements:
 ① Trial mix should be carried out according to the design requirements to determine the color of the concrete surface;
 ② The type and dosage of the admixture should be determined according to the test results of the concrete raw materials;
 ③ The environment of the project should be considered, and the mix design should be carried out according to the factors that affect the durability of concrete, such as anti-carbonization, anti-freeze damage, anti-sulfate, anti-salt damage, and inhibition of alkali-aggregate reaction;
 ④ When preparing fair-faced concrete, mineral admixtures should be used. Water brightener can be used to enhance the effect.
 2. Template engineering
 (1) The template blanking size should be accurate, the incision should be flat, and it should be leveled and straightened before assembly;
 (2) After the template is processed, it should be pre-assembled, and the flatness of the template, the overall size, the height difference between the adjacent panels, and the combination of the pull bolts should be checked;
 (3) Before the formwork is installed, the following work should be carried out: check the cleanliness of the panel; check the connection of the accessories inside the formwork, and the connection of the accessories should be firm; check the control line and elevation of the inner and outer formwork on the base; Uniform;
 (4) Formwork removal, the removal of fair-faced concrete formwork, in addition to complying with the current national standards "Code for Construction Quality Acceptance of Concrete Structure Engineering" GB50204 and "Technical Regulations for Large Formwork in Construction Engineering" JGJ74, should also meet the following requirements:
 ①The demolition time should be extended appropriately;
 ② Protective measures for fair-faced concrete walls and columns shall be formulated;
 ③ After the formwork is removed, it should be cleaned and repaired in time.
 3. Reinforcement works
 (1) The steel bar should be clean without obvious rust and pollution;
 (2) The reinforcement block should be arranged in a plum blossom shape, and the ends of the facing concrete positioning reinforcement should be painted with anti-rust paint, and should be covered with a plastic sleeve that is close to the color of the concrete;
 (3) Each intersection of steel bars should be bound, and the binding steel wire should not be less than two turns, and the buckle and the tail end should face the inner side of the component section, and should not touch the formwork or be too close to the formwork;
 (4) When the confronting bolts of facing fair-faced concrete collide with the steel bars, the principle of avoiding the tensioning bolts for the steel bars should be followed;
 (5) Measures such as waterproof shower should be taken after the steel bars are bound.
 4. Mixing and transportation of fair-faced concrete
 (1) Compulsory mixing equipment should be used when mixing fair-faced concrete, and the mixing time should be 20-30s longer than that of ordinary concrete;
 (2) The preparation environment and technical parameters of fair-faced concrete mixtures used within the same visual range should be consistent;
 (3) The working performance of the prepared clear-water concrete mixture should be stable, and there should be no bleeding and segregation phenomenon, and the slump loss over time for 90 minutes should be less than 30mm;
 (4) The slump value of the clear-water concrete mixture into the pump: the column concrete should be 150±20mm, and the concrete of the wall, beam and slab should be 170±20mm;
 (5) Special transport vehicles should be used for the transportation of fair-faced concrete mixture, and the container should be clean and free of water before loading;
 (6) Clear-water concrete mixture should not exceed 90 minutes from the end of mixing to before entering the mold;
 (7) The clear-faced concrete entering the construction site should be checked for slump one by one, and there must be no delamination or segregation.
 5. Pouring of fair-faced concrete
 (1) Before the fair-faced concrete is poured, the formwork should be kept clean and free of water;
 (2) When pouring vertical components, the interval time of layered pouring should be strictly controlled. Layer thickness should not exceed 500mm;
 (3) The openings of doors and windows should be poured with fair-faced concrete from both sides at the same time;
 (4) The fair-faced concrete should be vibrated evenly, and leakage, over-vibration, and under-vibration are strictly prohibited; the depth of the vibrating handle inserted into the surface of the lower concrete is greater than 50mm;
 (5) Before the subsequent fair-faced concrete pouring, loose stones or laitance layers at the construction joints should be removed first, and should be cleaned up after removal.
 6. Fair-faced concrete maintenance
 (1) The clear-faced concrete should be cured immediately after the formwork is removed, and the same curing measures should be adopted for the clear-faced concrete within the same visual range;
 (2) When clear-faced concrete is maintained, curing materials and curing agents that pollute the concrete surface shall not be used.
 7. Protection of fair-faced concrete products
 (1) The surface of ordinary clear-water concrete should be painted with transparent protective paint; the surface of finished clear-water concrete should be painted with transparent protective paint, and the paint should be a transparent paint that can protect the concrete surface, and should have anti-pollution, hydrophobicity, and water resistance ;
 (2) The construction process of coatings in the same visual range should be consistent.
 Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.