How To Control Ground-Based Ground Cracking

    Technical objective: Through standardized technical management, precise process control, and scientific risk prediction, quality and safety hazards such as collapse, cracking, and leakage in concrete projects are eliminated from the technical level, ensuring the safety of personnel, equipment, and structures during the construction process, and guaranteeing that concrete projects comply with the "Code for Acceptance of Construction Quality of Concrete Structures" (GB50204) and relevant safety production regulations. ​ Scope of application: This measure is applicable to the entire life cycle of concrete engineering, including all links such as the selection of concrete raw materials, mix proportion design, mixing and transportation, pouring and vibration, curing and formwork removal, covering various concrete structure projects such as housing construction, municipal works, Bridges and tunnels. ​ Raw material selection and inspection: Strictly screen raw materials such as cement, sand and gravel, admixtures, and admixtures. Select cement products that meet the design strength grade (such as P.O42.5 and above), and the sand and gravel gradation should comply with the specification requirements (the particle size of the gravel is determined based on the structural dimensions, with the maximum particle size not exceeding 1/4 of the minimum cross-sectional size of the component). After each batch of raw materials arrives at the site, a third-party testing institution is entrusted to conduct performance tests (such as cement strength and stability, mud content and crushing value of sand and gravel, water reduction rate and setting time of admixtures). Only after passing the tests can they be used. ​ Technical requirements for raw material storage: Cement should be stored in a closed warehouse, stacked in zones according to the batches entering the site, and kept at least 30cm above the ground to prevent moisture and caking. The sand and gravel yard is hardened and treated, with rain shelters set up. Sand and gravel of different specifications are stored separately to avoid mixing. Admixtures are stored in dedicated tanks and labeled to prevent confusion with other materials. ​ Customized mix ratio: According to the type of engineering structure (such as beams, slabs, columns, foundations), strength grade (such as C30, C40), construction environment (temperature, humidity) and construction technology (pumping, self-compaction), entrust a qualified laboratory to design a special mix ratio. Clarify key parameters such as water-binder ratio, sand ratio, and admixture dosage (for example, the slump of pumped concrete should be controlled at 120-160mm, and the spread of self-compacting concrete should be ≥550mm). ​ Mix proportion optimization technology: By adding admixtures such as fly ash and mineral powder, the amount of cement is reduced, the heat of hydration is lowered, and temperature cracks in mass concrete are avoided. For winter construction, early-strength admixtures should be added to the mix proportion to ensure the early strength growth of concrete. During summer construction, adjust the dosage of retarder, extend the initial setting time, and prevent the initial setting of concrete during transportation. ​ Plan formulation and review: Prepare a special construction plan for concrete projects, clearly defining the construction process, technical parameters (such as the thickness of each pouring layer, vibration time, and curing period), and quality and safety control points. For special projects such as large-volume concrete (pouring volume ≥1000m³ or thickness ≥1m), ultra-high pumping concrete (pumping height ≥100m), and special-shaped structure concrete, experts are organized to conduct technical arguments on the plans, with a focus on reviewing temperature control, support systems, and distribution methods, etc., to ensure the scientific and feasible nature of the plans. ​ Technical briefing and Training: After the plan is approved, a comprehensive technical briefing will be conducted for technical personnel and construction teams, detailing the mix ratio requirements, pouring sequence, vibration key points, and emergency response measures. Organize technical training for operators, conduct practical exercises on key procedures such as the use of vibrators and the connection of pumps and pipes, and only allow them to take up their posts after passing the assessment. ​   Technical supervision of the mixing process: The mixing plant adopts a fully automatic metering system to ensure that the metering deviation of raw materials complies with the specification requirements (the metering deviation of cement and admixtures is ≤±1%, and that of sand and gravel is ≤±2%). The mixing time should be strictly controlled (for ordinary concrete, the mixing time should be ≥90 seconds; for concrete with admixtures or admixtures, it should be ≥120 seconds). During the mixing process, technicians should be arranged to inspect and observe the workability of the concrete (such as slump, cohesion, and water retention). If problems such as segregation and bleeding occur, the mix proportion should be adjusted immediately or the mixing should be stopped. ​ Technical support during transportation: Special tank trucks are used for concrete transportation. The inner walls of the tank trucks are thoroughly cleaned to prevent residual concrete from affecting the quality of fresh concrete. The transportation route should be planned in advance to avoid congested sections and ensure that the transportation time is ≤ the initial setting time of the concrete (≤2 hours at normal temperature and ≤1.5 hours at high temperature). During transportation, the tanker should maintain a low rotational speed (2-4r/min) to prevent concrete segregation. After the concrete arrives, technicians will test the slump on site. If the deviation exceeds ±20mm, the laboratory will issue an adjustment plan. It is strictly prohibited to add water at will. ​ Pouring sequence technical optimization: Follow the principle of "layered pouring, symmetrical advancement, and continuous operation". The concrete pouring of beams and slabs should be advanced from one end to the other, while the concrete pouring of columns and walls should be done layer by layer, with each layer thickness ≤500mm (when using insert-type vibrators), to avoid local accumulation causing overloading of formwork supports. The "inclined plane layering" pouring method is adopted for mass concrete, with a layering thickness of 300-500mm. The pouring speed is controlled (generally ≤2m/h) to reduce internal temperature stress. ​ Vibration Technical:  Specification The type of vibrator should be selected based on the slump of the concrete (high-frequency vibrators should be used for a smaller slump, and medium-frequency vibrators for a larger slump). When using an insertable vibrator for vibration, the spacing between the vibration rods should be no more than 400mm, and the insertion depth should be 50-100mm to the lower layer of concrete. The vibration time should be controlled at 15-30 seconds (until the concrete surface shows slurry and no air bubbles escape). Over-vibration (to prevent aggregate segregation) or missed vibration (to avoid honeycomb and pitted surfaces) is strictly prohibited. During the vibration process, avoid the vibration rod touching the steel bars, formwork and embedded parts to prevent structural deformation or displacement of embedded parts. ​ Temperature control for bulk concrete: The "internal reduction and external protection" technical measure is adopted. Temperature measurement tubes are pre-embedded inside (with one temperature measurement point set every 50-100 square meters) to monitor the internal and surface temperatures of the concrete in real time, with the temperature difference controlled at ≤25℃. Circulating cooling water can be introduced inside to lower the core temperature. The surface is covered with thermal insulation cotton and plastic film to reduce heat loss and prevent temperature cracks. When the temperature difference exceeds the limit, add insulation layers or adjust the flow rate of cooling water. ​ Conventional concrete moisture control: Within 12 hours after the concrete pouring is completed, cover it with moisture-retaining materials (such as gunny bags, geotextiles). During the hot summer, water it in time for maintenance to keep the surface moist. During winter construction, methods such as covering with electric blankets and steam curing should be adopted to ensure that the curing temperature is ≥5℃. The curing time should be carried out in accordance with the specifications (≥7 days for ordinary concrete, ≥14 days for concrete with retarding admixtures or with impermeability requirements) to prevent shrinkage cracks caused by rapid water loss in the concrete. ​   The determination of formwork removal time: The formwork removal time is determined based on the strength of the concrete test blocks under the same curing conditions. For bending members such as beams and slabs, formwork removal can only be carried out when the strength of the test blocks reaches 75% (for spans ≤8m) or 100% (for spans > 8m) of the designed strength. For vertical components such as columns and walls, the side formwork can be removed when the strength of the test block is ≥1.2MPa. Before formwork removal, technicians should issue a formwork removal application, which can be implemented after approval by the supervision unit. It is strictly prohibited to remove formwork in advance, which may cause structural cracking or collapse. ​ Technical Specifications for formwork removal operations: Formwork removal follows the principle of "install first and then remove, install later and then remove first, from top to bottom". Rough formwork removal is strictly prohibited. When removing large formwork, a crane should be used for hoisting, and a dedicated person should be assigned for command. No one is allowed to stand under the formwork. After formwork removal, promptly clean up the residual concrete on the surface of the formwork, check the flatness and deformation of the formwork, and repair the damaged parts before putting it back into use. ​ Structural entity inspection: 28 days after the concrete pouring is completed, a third-party inspection agency is entrusted to conduct structural entity inspection, including concrete strength rebound, steel bar cover thickness inspection, structural dimensional deviation inspection, etc. Conduct core drilling and sampling tests on large-volume concrete and important components (such as frame columns and main beams of Bridges) to ensure that the concrete strength meets the design requirements. For the parts that fail the inspection, a special treatment plan shall be formulated and implemented after being approved by the design unit (such as reinforcement by high-pressure grouting, external concrete coating, etc.). ​ Defect repair technology: For defects such as honeycomb, pitted surface and exposed bars on the concrete surface, the "surface treatment method" is adopted for repair: Clean the loose concrete at the defect area, rinse it clean with a high-pressure water gun, apply an interface agent, and then repair it with fine aggregate concrete or mortar in the same proportion as the original concrete. After repair, cover and maintain it. For crack defects, the repair method should be selected based on the crack width (surface sealing method for width ≤0.2mm, pressure grouting method for width > 0.2mm). During the repair process, technical records should be kept well to ensure the repair quality. ​ Establish technical archives for concrete engineering, collect and organize raw material inspection reports, mix proportion notices, construction logs, temperature measurement records, curing records, formwork removal applications, physical inspection reports and other materials to ensure that the materials are complete, accurate and traceable. Technical archives are filed and preserved in accordance with the prescribed requirements, serving as an important basis for project acceptance and later maintenance. ​ Regularly review and analyze the technical data of concrete engineering, summarize the technical problems during the construction process (such as the optimization effect of mix proportion and the accuracy of temperature control), form a technical summary report, provide technical references for subsequent similar projects, and continuously improve the safety production technology level of concrete engineering. ​   Emergency technology for concrete supply interruption: If the supply of concrete is interrupted due to a malfunction of the mixing plant or traffic congestion, immediately stop pouring, vibrate and compact the surface of the already poured concrete, and cover it with moisture-retaining materials. When the interval time exceeds the initial setting time of the concrete, handle it according to the requirements of the construction joint (set up a vertical construction joint, clean the surface floating slurry and loose aggregates, and apply an interface agent). After the concrete supply is restored, re-pour to ensure that the construction joint is tightly combined. ​ Emergency techniques for structural cracks: If early cracks are found on the concrete surface during the pouring process, stop pouring immediately, check the width and depth of the cracks. If they are surface dry shrinkage cracks, cover them with water in time and strengthen moisture retention and maintenance. If it is a temperature crack, add an insulation layer and adjust the temperature control measures. If the cracks continue to develop, immediately organize the evacuation of personnel, entrust the design unit to formulate a reinforcement plan, and adopt technical measures such as temporary supports and grouting sealing to prevent the cracks from expanding and causing structural safety accidents.   Instructions for Use: This plan is a general template. Before the specific implementation of each project, it should be refined and supplemented according to the characteristics of the project (such as super-high, super-heavy, large-span structures, etc.), especially the control measures for major hazard sources.    

– Disc concrete trowel: This type of trowel is usually equipped with one or more circular steel discs that grind and smooth the concrete surface by rotating. The discs can be fixed or adjustable to suit different construction needs. – Blade concrete trowel: Blade trowels use fan-shaped blades that are mounted on a rotating shaft. When the machine is running, the blades swing as the shaft rotates to polish and smooth the concrete surface. The angle of the blade is usually adjustable, which allows the operator to adjust the angle between the blade and the ground according to the state of the concrete to achieve the best smoothing effect. – Disc type: More suitable for larger areas of concrete surface treatment, especially when a large area needs to be covered quickly. It can provide good flatness and is suitable for the initial leveling stage. – Blade type: More effective in detail processing, edge processing and situations where higher precision is required. Blade type trowels can be used when the concrete is still in a relatively soft state to help improve the density and smoothness of the surface. – Disc type: Usually requires greater force to push or manipulate, especially when dealing with hard concrete. However, with the development of technology, there are now electric or gasoline-driven disc trowels, which greatly reduce the burden on the operator. – Blade type: Relatively speaking, blade trowels are more flexible to operate, especially for small projects or occasions with special requirements. Due to its design features, blade trowels distribute pressure on the ground more evenly during operation, which helps to reduce damage to the concrete surface. In short, which type of concrete trowel to choose depends on factors such as specific construction conditions, the type of work to be completed, and personal preference. In practical applications, these two types of trowels are sometimes used in combination to achieve the best construction results.

    The concrete laser leveling is a highly efficient construction device that uses a laser measurement and control system to achieve automatic leveling. Its core value lies in its ability to efficiently complete large-scale concrete floor construction with medium to high requirements for flatness, levelness, and density in a single operation. It primarily replaces traditional manual formwork and scraper leveling processes, delivering a qualitative leap in precision, efficiency, and overall integrity. Field Classification Typical scenarios Core requirements and equipment advantages 1) Industry and warehousing Automated logistics warehouses Requirements: Ensure smooth operation of AGVs, stackers, and forklifts; withstand heavy loads; be wear-resistant and dust-free. Advantages: Achieve extremely high flatness (e.g., ±3mm/3m), ensure uniformity over large areas, reduce equipment operation and maintenance costs, and provide seamless, high-strength flooring. Large industrial plants (automotive, electronics, pharmaceuticals, etc.) Production workshops and warehouses 2) Commercial and public facilities Large supermarkets/shopping malls Requirements: Balance comfort, safety, and aesthetics; durability required in high-traffic areas; precise drainage slope required for parking lots. Advantages: Efficient and shortened construction schedule; precise slope control to prevent water accumulation; and a perfect, aesthetically pleasing base surface. Underground parking lot Airport terminal, high-speed rail station Exhibition centers, gymnasiums 3) Municipal administration and infrastructure Municipal roads, auxiliary roads, squares Requirements: Durability and impermeability; operation within specialized spaces (such as pipe corridors); extremely flat tank floor to ensure smooth water flow. Advantages: Small equipment adapts to narrow spaces; improved density and leak resistance; precise control of slope and flatness. Underground utility corridors/tunnel surfaces Sewage treatment plant/water plant tank bottoms 4) Special application scenarios Cold Storage Flooring Requirements: Low-temperature resistance to frost heave; providing a perfect base for high-end surface coatings. Advantages: Reduces cold bridge cracks; the flatness of the base determines the final effect and lifespan of the surface coating, so machine-leveling is the best option. Wear-Resistant Flooring/Epoxy Flooring Base Treatment Ultra-high precision: Flatness can reach ±2-3mm/3m, far exceeding manual accuracy. Extremely high efficiency: A single-day work area of ​​over 2,000 square meters can be completed, 5-10 times faster than manual labor, significantly shortening construction time. Improved integrity: Reduced construction joints avoid potential cracks and unevenness caused by block pouring. Increased floor strength: High-frequency vibration increases concrete density and improves wear and pressure resistance. Reduced labor costs: Automated operation reduces reliance on skilled workers and reduces labor intensity.   Despite its outstanding advantages, laser leveling machines are not omnipotent and may not be applicable or cost-effective in the following scenarios: For very small areas (e.g., <50 m2): Equipment delivery and commissioning costs may be higher than labor costs. For complex and irregularly shaped surfaces (e.g., multi-curved and undulating artistic floors): The equipment is suitable for regular flat or inclined surfaces, but complex shapes still require manual shaping. For temporary surfaces with very low strength requirements (e.g., temporary construction paths): High precision is not required; simple manual leveling can meet the requirements. For ultra-thick base construction: When pouring too thick a layer in one go, additional paving equipment may be required for preliminary paving.   Concrete laser leveling are a powerful tool in modern floor construction, with applications centered around the key concepts of "large-scale," "high precision," "high efficiency," and "high demands." With the rapid development of modern logistics, intelligent manufacturing, and large-scale infrastructure, they have rapidly gained popularity and become the mainstream and preferred equipment for industrial flooring, large public buildings, and municipal projects. When selecting a laser leveling, a comprehensive assessment should be made based on the specific project area, precision requirements, budget, and construction schedule.   ARMOUR JOINT CONCRETE LASER LEVELING MACHINE POWER TROWEL SLIPFORM MACHINE STEEL FIBER TOPPING SPREADER