Selecting the right low-cement refractory castable requires a comprehensive assessment based on the core requirements of the application, combining performance indicators, raw material characteristics, and construction conditions. The key approach is "Application Matching → Performance Screening → Detailed Verification." The specific steps are as follows:

1. Identify the Core Application Conditions (First Prerequisite)

First, identify the key parameters of the application scenario; this forms the basis for all selections:

1. Temperature Conditions: Determine the long-term operating temperature (e.g., 1200°C for kiln lining vs. 800°C for pipe insulation), short-term peak temperature, and frequency of temperature fluctuations (which determine thermal shock stability requirements).

2. Media Environment: Determine whether the castable will be exposed to corrosive media (acidic/alkaline gases, molten metal/slag), abrasive materials (dust, particle erosion), or humid, high-temperature, and high-pressure environments.

3. Load and Structure: Determine whether the castable will bear loads (e.g., the kiln mouth, brick support plate), whether it will be subject to vibration and impact, and the structural dimensions (thin walls vs. thick linings, which affect volume stability requirements).

4. Construction Constraints: Determine whether there are forced mixers and vibrating equipment on site, whether the construction space is confined (affecting fluidity requirements), and the curing conditions (normal temperature curing vs. low/high temperature curing).

II. Matching Key Performance Indicators (Core Screening Criteria)

Based on the application requirements, prioritize 3-5 core performance indicators before selecting products:

1. High-Temperature Resistance: For high-temperature applications (≥1000°C), corundum and mullite aggregates are preferred, combined with a high-alumina cement + silica fume matrix. For medium- and low-temperature applications (≤800°C), economical aggregates such as clay clinker and fly ash can be used.

2. Thermal Shock Stability: For applications with frequent temperature fluctuations (such as metallurgical furnaces), select aggregates with a low thermal expansion coefficient (such as silicon carbide and cordierite), or optimize grading to reduce internal stress. Thermal shock stability (water-cooled at 1100°C) of 15 or more is required.

3. Erosion/Abrasion Resistance: For corrosive environments, choose an acid-resistant/alkali-resistant matrix (such as silica powder or magnesia aggregate). For abrasive environments, choose a high-hardness aggregate (such as brown corundum or silicon carbide), with an aggregate content of ≥70%.

4. Mechanical Properties: For load-bearing structures, the compressive strength must be ≥40 MPa at room temperature and ≥20 MPa at high temperature (operating temperature). For non-load-bearing structures, the compressive strength can be reduced appropriately, but adhesion must be guaranteed.

5. Construction and Volume Stability: For narrow spaces or pumping applications, high fluidity (slump ≥200 mm) and no segregation are required. For thick linings or large-scale casting, low shrinkage (28-day drying shrinkage ≤0.15%) is required. Products containing expansion agents are preferred.

3. Verify the rationality of raw materials and mix proportions (performance assurance)

1. Aggregates: Continuously graded aggregates with a mud content ≤1% and a water absorption rate ≤1.5% are preferred. The aggregate type should also be compatible with the operating temperature (e.g., corundum should withstand temperatures exceeding 1600°C, while clay clinker should withstand temperatures around 1000°C).

2. Matrix: The cement content must meet the definition of "low cement" (typically ≤8%), with aluminate cement (high-temperature resistance) or sulfoaluminate cement (early strength) preferred. The active micropowder (silica fume, ultrafine alumina powder) should be moderate (10%-20%). Excessive additions can lead to poor flowability.

3. Admixtures: Verify the inclusion of compatible high-efficiency water-reducing agents (e.g., polycarboxylic acid-based, to ensure a low water-cement ratio), retarders (to adjust setting time), or dilatants (to compensate for shrinkage) to avoid incompatibility between the admixture and the matrix.

IV. Combining Practicality and Economy (Key to Implementation)

1. Construction Compatibility: If vibrating equipment is unavailable on-site, select a flow-type low-cement castable. If curing conditions are poor (e.g., low temperatures), prioritize products containing early-strength agents and requiring no complex curing.

2. Supplier Assurance: Select suppliers with industry references (such as application cases for similar kilns and equipment) and require performance test reports (focusing on high-temperature strength, thermal shock stability, and shrinkage). Prioritize manufacturers that can provide customized mixes (e.g., adjustments for special media).

3. Economic Balancing: For medium- and low-temperature, non-corrosive conditions, economical products with a clay clinker + fly ash matrix can be selected. For high-temperature, highly corrosive conditions, prioritize performance and select high-end products with corundum + highly active micropowder.

Core Summary
The selection process can be simplified as follows: First, determine the operating conditions (temperature, media, structure) → Target core performance (high-temperature resistance/corrosion resistance/thermal shock resistance) → Core material mix (aggregate, matrix, admixtures) → Balance construction and cost. The ultimate goal is to ensure that the "performance shortcomings" of the castable are not lower than the minimum requirements of the working conditions, while avoiding cost waste caused by excessive pursuit of high-end indicators.