Refractory castables, as the key lining material for industrial furnaces, directly impact the service life of thermal equipment and production safety through their construction quality. During winter construction in low-temperature environments, material performance, construction techniques, and quality control face significant challenges. This guide systematically presents a comprehensive technical solution for winter refractory castable construction. It covers pre-construction preparation, raw material control, temperature management, specific construction steps, curing methods, and emergency response measures. Its purpose is to assist engineering technicians in ensuring construction quality under low-temperature conditions, preventing material performance degradation and structural damage caused by freezing damage.

Challenges and Basic Requirements for Winter Construction

Winter construction of refractory castables presents a series of unique challenges. As ambient temperatures drop, both the physical properties of the materials and their chemical reaction processes undergo significant changes, ultimately affecting the quality of the final formed structure. According to relevant specifications, when the outdoor daily average temperature remains consistently below 5°C for five consecutive days, the project enters the winter construction phase, necessitating special measures. This temperature threshold is established based on extensive engineering practice and materials science research, as refractory castables begin exhibiting noticeable performance changes at this temperature.

Mechanism of Low Temperature Effects on Castable Refractories

The primary effects manifest in the following aspects: First, low temperatures significantly prolong the hydration reaction time of cement, resulting in slow strength development. When temperatures drop below 0°C, free water within the material begins to freeze, expanding by approximately 9% in volume. This expansion generates internal stresses that disrupt the formed structural framework. At temperatures as low as -15°C, nearly all free water freezes, causing the hydration reaction to cease entirely. Second, the flowability of castables decreases at low temperatures, leading to uneven mixing and increasing the likelihood of voids and defects during construction. Furthermore, frozen castables exhibit surface frost patterns, uneven whitening, prone cracking at edges and corners, and the formation of numerous internal pores, resulting in near-total loss of bond strength with anchoring components.

Basic temperature requirements for winter construction include: ambient temperature must not fall below 5°C; castable material temperature upon placement should not be lower than 10°C; and surfaces in contact with the castable must maintain a temperature of at least 5°C. These temperature standards are essential prerequisites for ensuring proper material hydration and stable structural formation. It is important to note that different cement types have varying temperature requirements: mixing water temperature for Portland cement castables must not exceed 60°C, while for aluminate cement castables, it must not exceed 30°C.

Weather monitoring and contingency plan activation are prerequisites for winter construction. Construction sites should install fully automated weather stations to monitor parameters such as air temperature, wind speed, and humidity in real time. When a cold wave is forecasted or the daily average temperature falls below 5°C for five consecutive days, the winter construction contingency plan must be immediately activated. Given the critical importance of temperature monitoring, multiple measurement methods are recommended, including equipping with a far-infrared thermometer (range: -30°C to 300°C, accuracy: ±1°C) to ensure data accuracy and reliability. Concurrently, a 48-hour cold wave warning mechanism should be established to allow sufficient time for implementing protective measures.

Comprehensive preparatory work prior to construction

The success of winter refractory castable construction largely hinges on the thoroughness of preliminary preparations. This phase requires systematic planning and implementation across four dimensions: technical, material, site, and personnel. Adequate preparation not only effectively addresses low-temperature challenges but also prevents potential quality issues, ensuring smooth construction processes.

Technical preparation forms the core of pre-construction work. This includes detailed thermal calculations. In accordance with the “Code for Winter Construction of Building Engineering,” conduct a temperature loss analysis throughout the entire process of mixing, transporting, and pouring the castable. Determine the heating temperatures and insulation measures for each stage. Typical thermal calculation parameters indicate: when the ambient temperature is -5°C, mixing water must be heated to 65°C–70°C; aggregate preheating temperature should not be lower than 5°C; temperature loss during transportation should be controlled within 3°C/h. Simultaneously, specialized winter construction plans and operation manuals for different sections must be developed, specifying technical parameters such as anti-freeze admixture methods, thermal curing temperature curves, and critical strength requirements. Technical briefing is crucial for ensuring plan implementation. All construction personnel must undergo specialized winter construction training, focusing on temperature monitoring essentials and emergency response measures. Only those who pass the assessment may proceed to the job site.

Site Preparation: Involves setting up heating and insulation facilities, which form the material foundation for coping with low-temperature environments. The mixing plant must erect an insulated shed (recommended dimensions: 15m × 8m × 4m) and utilize fuel-fired heaters (e.g., two 20kW units) for heating, maintaining an internal temperature above 15°C. Heated water tanks (3m³ capacity) should be equipped with fully automatic electric heating rods (total power 36kW) and precise temperature control systems (accuracy ±2°C) to ensure stable water temperature. Aggregate silos require double-layer color-coated steel panels with 50mm rock wool insulation, and underfloor heating pipes (hot water circulation temperature 50°C~60°C) should be installed at the base to prevent aggregate freezing. For large industrial furnace construction, cover air leaks in the furnace body with canvas or plastic sheeting to block cold air intrusion and create a relatively warm working environment.

Material Reserves: Plan ahead with excess quantities for three major material categories:

– Insulation materials (e.g., 500 flame-retardant cotton blankets, 2m×3m, thermal conductivity λ≤0.04W/m·K; 1000m of electric heating cable, 20W/m power rating; 300m² waterproof canvas), temperature measurement equipment (e.g., 4 far-infrared thermometers), and emergency supplies (1 50kW diesel generator, 50m spare heating pipe, 100 quick-response thermocouples, and antifreeze reserves at 120% of the design quantity). Particular attention must be paid to ensuring all insulation materials possess flame-retardant properties, as heating equipment is frequently used during winter construction, posing elevated fire risks. Auxiliary materials such as formwork and anchoring components should also be transported into heated storage facilities in advance to prevent low temperatures from compromising their performance or causing installation difficulties.

Personnel organization and training constitute the human resource foundation for ensuring proper implementation of all measures. Winter construction requires establishing a specialized temperature control team responsible for 24-hour monitoring and recording of temperature data, as well as operating heating equipment. All construction personnel must undergo specialized winter construction training covering: antifreeze additive procedures, standard temperature monitoring protocols, and emergency response procedures. Training should incorporate assessment systems to ensure every operator fully understands the specific requirements and operational standards for low-temperature environments. It is recommended to appoint dedicated winter construction quality supervisors to continuously monitor temperature control and process execution throughout construction, promptly correcting non-compliant operations.

Pre-construction site inspections and acceptance are equally indispensable. This includes: verifying the integrity of heating equipment, ensuring insulation facilities are airtight, calibrating temperature measurement instruments, and confirming emergency supplies are in place. Particular attention must be paid to anchorage inspections. Heat-resistant nails must be used for areas above 500°C, and anchorage surfaces should be coated with 0.5-1mm thick paint or wrapped with plastic tape to cushion thermal expansion forces. Formwork systems must ensure dimensional accuracy, structural stability, tight joints, and complete removal of internal debris. Only after thorough pre-construction inspection and acceptance can winter concrete pouring operations actually commence.

Raw Material Control and Proportioning Management

Quality control for winter construction of refractory castables begins with raw material selection and processing. Low-temperature environments impose stricter requirements on the storage, preheating, and proportioning of various raw materials. Proper raw material management not only ensures smooth construction progress but also forms the foundation for achieving the designed performance of the final lining. Addressing the characteristics of winter construction necessitates systematic control across four aspects: material performance indicators, storage conditions, preheating treatment, and proportioning adjustments.

Raw material performance indicators are the primary consideration when selecting materials for winter construction. For cementitious materials, early-strength ordinary Portland cement (P·O42.5R) is recommended, with a 3-day compressive strength ≥25MPa and cement storage temperature ≤60°C. Calcium aluminate cement (e.g., CA-70 type) must meet technical requirements of initial setting time ≥45 minutes and final setting time ≤300 minutes, with storage temperatures maintained above 5°C. Aggregate quality control is equally critical: High-alumina bauxite aggregate (two-grade mix: 5-10mm and 10-20mm) must have clay content ≤0.5% and zero frozen lumps; Silica fume (≤0.088mm) must contain ≥95% SiO₂ with moisture content ≤0.3%; Brown fused alumina fine powder (325 mesh) must have an Al₂O₃ content ≥90% and a specific surface area ≥350m²/kg. These indicators directly impact the construction performance and ultimate strength of the castable, necessitating stricter control during winter construction conditions.

Material Storage Management: This is particularly critical in low-temperature environments. Upon arrival at the site, refractory castables must be stored in a rainproof warehouse or construction facility, selecting a location that is elevated and dry. It is best to lay wooden pallets on the ground during storage to prevent moisture absorption. For bagged materials, inspect packaging integrity; materials that are opened, damaged, or damp must not be used. Materials from different manufacturers must never be mixed. Even similar materials should be stored separately with clear labeling. Crucially, refractory materials showing clumping or water seepage inside bags are prohibited for use. However, clumps formed during transportation that can be easily broken apart by gentle rubbing do not affect performance. Cement storage requires moisture-proof measures and should not exceed a 3-month storage period to prevent reduced reactivity from prolonged storage.

Raw Material Preheating: A critical step unique to winter construction. Per specifications, mixing water must be heated first, with temperatures controlled based on cement type: – Water temperature for 42.5 and higher ordinary Portland cement refractory castables must not exceed 60°C (140°F). – Water temperature for aluminate cement refractory castables must not exceed 30°C (86°F). When water heating alone fails to meet temperature requirements, supplementary heating of aggregates may be employed. However, upper temperature limits also vary by cement type: aggregate heating for ordinary Portland cement castables must not exceed 40°C, while for aluminate cement castables, it must not exceed 30°C. Recommended aggregate heating methods include indirect heating via heated beds, exhaust pipe ventilation, or steam. Direct heating with open flames is strictly prohibited. After preheating, all raw materials should be used promptly to minimize prolonged storage and heat loss.

Optimizing mix proportions is crucial for low-temperature construction. During winter operations, strictly adhere to the designed mix ratio for castables. Accurate measurement is essential: weigh cement, aggregates, and powdered materials by mass; measure water and additive solutions by volume. Considering the impact of low temperatures on material properties, three mix adjustments may be made under professional guidance: First, add appropriate amounts of setting accelerators to shorten setting time and prevent freezing due to slow solidification. For optimal results, this should be synchronized with water temperature heating. Second, strictly control water content, minimizing it while ensuring workability for vibration. Typically, adhere to the water-to-cement ratio specified in the product manual. Third, incorporate antifreeze agents when necessary (subject to manufacturer approval), but strictly prohibit the unauthorized addition of cement, limestone, or other unapproved admixtures.

Material inspection and testing procedures are more stringent during winter. Before construction, conduct a visual inspection of refractory castables; discard any contaminated or moisture-damaged materials. Mixing water must comply with Drinking Water Standards, with a temperature between 5°C and 40°C, chloride ion content not exceeding 50 ppm, and a pH value between 6.5 and 7.5. For the “hand-kneading” test method: If the ball deforms and flows through the gaps between fingers, it indicates excessive moisture content; if the ball cracks and disintegrates, the moisture content is insufficient. It is recommended to conduct small-scale trial mixing first to verify the material’s construction performance and setting characteristics in low-temperature environments. Adjust the mix ratio or process parameters as necessary. Complete process parameters should be recorded for each mixing operation, including material temperature, ambient temperature, water-to-material ratio, and mixing time, to provide a basis for quality traceability.

Temperature Control and Key Process Considerations During Construction

The construction process of winter-resistant refractory castables is a critical stage for quality formation. In low-temperature environments, temperature control and process details at every stage directly impact the final lining’s performance. Compared to normal-temperature construction, winter operations demand greater attention to the coordination and temperature maintenance across mixing, transportation, pouring, and vibration processes. This ensures materials complete hydration reactions and structural formation under suitable temperature conditions.

Mixing process control is the primary focus in winter construction. Mixing must be performed using forced-action mixers; manual mixing is strictly prohibited. Mixing areas should be located within heated shelters with ambient temperatures maintained above 5°C. Prior to mixing, add bulk materials (aggregates) followed by bagged materials (powders). Dry mix for 1-2 minutes before adding water for wet mixing. Water addition should occur in two stages: first incorporate 2/3 of the total water volume and mix for 1-3 minutes, then add the remaining 1/3 water and continue mixing. Total mixing time should generally be no less than 3 minutes but not exceed 5 minutes. For low-cement, ultra-low-cement, and cement-free castables, mixing duration critically affects physical properties. Batch size must be determined reasonably based on mixer capacity and work progress to prevent overloading (causing mixer jamming) or underloading (impeding efficiency).

Temperature monitoring and adjustment must be maintained throughout the entire mixing process. During winter construction, the following temperatures should be measured and recorded: the temperature of materials after heating in the heated shed, the temperature of the castable upon discharge from the mixer, and the temperature of the castable upon placement into the mold. The discharge temperature must ensure that the castable remains at least 10°C upon arrival at the mold after transportation. Temperature measurement points must be representative, with at least four readings taken per work shift. When using heated water, pay special attention to water temperature uniformity to prevent localized overheating causing false setting of cement. For aluminate cement castables, water temperatures exceeding 30°C may trigger rapid setting and must be strictly controlled. The temperature of the mixed castable can be quickly detected using an infrared thermometer. If insufficient temperature is detected, immediately adjust the preheating temperature of raw materials or inspect insulation measures.

Transportation and pouring coordination represent a critical weakness in winter construction. Mixed castable material should be promptly transported to the pouring location, ideally completing both transport and pouring within 15 minutes. Transportation equipment must incorporate insulation measures, such as using insulated tank trucks or covering with insulating blankets, to minimize temperature loss during transit. Minimize transport distances and transfer points to prevent segregation or freezing of the material. Prior to pouring, inspect formwork and anchorage components. For areas exposed to temperatures above 500°C, anchorages must be made of heat-resistant steel, coated with 0.5-1mm thick paint or wrapped with plastic tape to buffer thermal stress. Remove all debris from formwork cavities. Ensure ambient temperature remains above 5°C during pouring.

Pouring and vibration operations require high efficiency and precision. After pouring the refractory material into the formwork, promptly vibrate it with a vibrator. Vibration must be uniform. Once the surface slurry becomes fluid, slowly move the vibrator at a speed controlled between 1-2 meters per minute. For layered pouring, each layer should not exceed 300mm in thickness. The lower layer must be covered by the upper layer before initial setting. During compaction, avoid excessive vibration that could cause material segregation. Ensure thorough compaction at edges and corners to eliminate air pockets. In low-temperature conditions, the flowability of the castable may decrease. Adjust vibration parameters (e.g., frequency and duration) as needed, but never increase water content to improve flowability. The entire pouring process must be completed within 20 minutes. Any material that has begun initial setting must be discarded; adding water to re-mix and reuse is strictly prohibited.

Special attention is required for specific areas. For unique locations such as furnace roofs and suspended arches, the spray application method may be used, provided the ambient temperature remains above 5°C. If necessary, preheat the pouring surface with hot air. Expansion joints must be installed per design specifications and securely filled with specialized materials to prevent thermal contraction cracking at low temperatures. During construction interruptions, insulate the poured surface. When resuming work, heat the surface layer of the poured material to above 5°C and remove any potentially frozen surface material. Complex areas like pipes and openings require careful compaction using specialized tools to ensure density and eliminate voids.