With temperatures dropping recently, many construction projects have been affected. While refractory products are generally less affected, today we’ll focus on unshaped refractory castables.

We’ve previously discussed precautions for installing refractory castables in winter. Some companies may consider these less important, but in fact, several national standards contain specific regulations regarding the winter installation of refractory castables. Today, we have excerpted the relevant requirements from GB50211-2014, “Code for Construction and Acceptance of Industrial Furnace Masonry Works,” and CECS27-2016, “Technical Specifications for Winter Construction of Cement-Based Refractory Castables for Industrial Furnaces,” to discuss the issues surrounding the winter construction of refractory castables.

The “Code for Construction and Acceptance of Industrial Furnace Lining” contains the following provisions under “Winter Construction”:

1 Winter construction should commence when the daily average outdoor temperature remains below 5°C for five consecutive days; winter construction should be terminated when the daily average outdoor temperature remains above 5°C for five consecutive days.

2 In addition to complying with the provisions of this chapter, winter construction of industrial furnace masonry projects shall also comply with the provisions of other chapters of this code.

3 Winter masonry work on industrial furnaces shall be carried out in a heated environment.

4 When laying ordinary clay bricks for external flue ducts of industrial furnaces using cement mortar, the heat storage method may be employed.

5 During the masonry work of industrial furnaces, the temperature at the work site and around the masonry shall not be lower than 5°C. If the furnace cannot be fired up and put into operation immediately after completion of the masonry work, drying measures shall be taken to remove all moisture from the furnace lining.

6 Refractory bricks and precast blocks shall be preheated to above 0°C prior to masonry work.

7 The temperature during the application of refractory mortar, refractory plastic, refractory spray coatings, and cement-bonded refractory castables shall not be lower than 5°C. The temperature during the application of clay-bonded refractory castables, water-glass refractory castables, and phosphate refractory castables should preferably not be lower than 10°C.

8 During winter construction, the mixing of refractory mortar and refractory castables shall be carried out in a heated shed. When transport distances are long, thermal insulation measures shall be taken. Materials such as cement and formwork shall preferably be transported into the heated shed in advance for storage.

9 The mixing water for refractory castables shall be heated. The heating temperatures are as follows: for silicate cement refractory castables, the water temperature shall not exceed 60°C; for aluminate cement refractory castables, the water temperature shall not exceed 30°C. Cement shall not be heated directly.

10 No setting accelerators shall be added during the construction of refractory castables.

11 Curing of cement-based refractory castables may be performed using the heat retention method or the heating method. The heating temperature for silicate cement refractory castables shall not exceed 80°C, and for aluminate cement refractory castables, it shall not exceed 30°C.

12 Curing of clay, water glass, and phosphate refractory castables shall be performed using the dry heat method. The heating temperature for water glass refractory castables shall not exceed 60°C.

13 During spray application, refractory spray mixes and water shall be preheated before mixing, and insulation measures shall be taken for the spray mix pipes, water pipes, and the furnace (or pipe) shell being sprayed.

14 During winter construction, specific construction records shall be maintained and shall comply with the following provisions:

① The outdoor air temperature, the temperature at the work site and around the masonry, the temperature of heated materials inside heated shelters, and the temperature of unshaped refractory materials during mixing, application, and curing shall be measured every 4 hours;

② All measurement points shall be numbered, and a layout diagram of the temperature measurement points shall be drawn;

③ When measuring the temperature of unshaped refractory materials, the thermometer shall be left in the material for no less than 3 minutes.

The “Technical Specification for Winter Construction of Cement Refractory Castables for Industrial Furnaces” contains the following relevant provisions for the construction of refractory castables in winter:

This provision primarily applies to industrial furnaces with refractory castables whose linings use aluminate cement or silicate cement as binders. This excludes water glass refractory castables and phosphate and phosphatic refractory castables, as these two types of castables have strict requirements regarding ambient temperature during installation; they do not set at low temperatures and are not suitable for installation during winter. It also excludes non-hydraulic refractory castables such as alumino-magnesian refractory castables, steel fiber refractory castables, acid-resistant refractory castables, and clay-bonded refractory castables.

Aluminate cement, silicate cement, and ordinary Portland cement can all be used as binders for refractory castables in summer. However, in winter, it is recommended to prioritize the use of aluminate cement, as it features rapid setting, high strength, refractory properties, and resistance to sulfate attack, making it an excellent binder for cement-based refractory castables during winter construction. The main varieties include CA-50 cement, CA-60 cement, CA-70 cement, and CA-80 cement. Other types, such as slag silicate cement, pozzolanic silicate cement, and fly ash silicate cement, may also be used, provided their strength grade is no less than 42.5. In particular, when using cement with low early strength for winter construction, the strength grade should not be lower than 42.5.

During the mixing of refractory castables, wastewater, seawater, or water containing harmful impurities must not be used. On the one hand, this would affect the workability and hardening process of the castable; on the other hand, it would reduce the high-temperature performance of the refractory castable, preventing it from meeting specifications. The chloride ion concentration in the water used should not exceed 300 mg/L.

During the casting process, the temperature of the surface in contact with the castable is often overlooked. While the temperature of the castable itself can be controlled during winter construction, if the temperature of the contact surface is too low, it will cause the temperature of the freshly poured castable to drop rapidly, thereby affecting the development of the cast body’s strength. This is because standards stipulate that the temperature of the surface in contact with the refractory castable must not be lower than 5°C.