The design of the physical properties of the new refractory mud mainly focuses on the following five aspects:
 
1 Bonding time and bond strength of new fireclay cement
The construction performance of refractory mud is a difficult problem to solve. In the past, as long as the chemical composition of the refractory mud passed the test, it was judged to be qualified, but the construction unit was more concerned about the construction performance of the mud. This is not only from the ease of use of refractory mud, but also the construction performance of the mud has a great influence on the quality of the masonry.

At present, from the perspective of the physical properties of refractory mud, there are two indicators worth paying attention to: one is the bonding time; the other is the cold flexural bond strength after drying at 110 °C. The bonding time measures the adjustable time of the brick body during the masonry process, and also indirectly reflects the fullness of the mud in the brick joints. If the bonding time is too short, the adjustable time of the bricks is limited, and the quality of masonry is difficult to guarantee; if the bonding time is too long, the fixing time of the masonry will be prolonged, which will affect the construction progress and efficiency, and increase the amount of mud from the brick joints. Possibility to flow. The cold flexural bond strength after drying at 110 ℃ directly affects the overall strength of the masonry at room temperature, which is very important for the protection of the masonry from the construction process to the oven. After drying, the strength of the mud is low, and it is easy to loosen and fall off after being subjected to vibration and load during construction, thereby causing cracks in the cracks of the bricks or dislocation of the bricks. In the "Compilation" in the 1990s, specific regulations were made for these two indicators. The bonding time is generally 1 to 3 minutes, and the cold flexural bond strength after drying at 110 °C is 0.5 to 2.0 MPa. The refractory mud that reaches the above indicators has good construction performance and stable masonry quality.

It is worth mentioning that, in practical applications, the main thing of practical significance is the thermal bond strength. However, in the "Compilation" in the 1990s, there is an index of cold flexural bond strength after burning. The high index can only indicate that the refractory mud produces more melts at the firing temperature, but its thermal flexural bond strength is low. This should be taken into account when designing refractory slurries.

2 Particle size composition of new fireclay cement
According to the size design and practice of standard bricks in my country, the joints of bricks are generally 1-2mm. Combined with other requirements, there are generally two provisions for the particle size of refractory powder in refractory mud: one is the critical particle size, and the other is the proportion of fine powder ≤ 0.074 mm. The critical particle size is too large, which can neither guarantee the width of the joints nor adjust the flatness of the bricks. At present, the critical particle size is generally less than 1/4 of the brick joint, that is, 0.25 to 0.50 mm. The overall particle size of refractory mud tends to become finer, which is beneficial to the improvement of construction performance on the one hand, and prevents particle segregation on the other hand.

In the "Compilation" in the 1990s, it is generally stipulated that the mass fraction of fine powder ≤0.074mm is ≥50%. When designing the particle size composition of the refractory slurry, it is better if the close packing between the particles in the refractory powder can be considered.

3 Softening temperature under load, creep and refractoriness of fireclay cement
In large-scale high-temperature furnaces, the masonry in some parts is subjected to considerable loads. In this case, the load softening temperature and creep of refractory mud become important basis for structural design. With the development of technology, mud is mixed with various additives, some of which will affect the softening temperature and creep range of mud under load. This factor should be taken into account when designing refractory mud. In addition, particle size distribution also affects its softening temperature under load and creep.
 
The refractory degree of refractory mud is an index to intuitively evaluate its refractory performance, and can be used to evaluate the refractory grade of refractory mud of the same material. Like the first two, this index is usually related to the chemical composition of the refractory powder and the type and amount of additives.

4 Thermal expansion and contraction of fireclay cement
The expansion or contraction of the mud during the heating process has a great influence on the tightness and integrity of the masonry. When designing the expansion performance of the mud, it should be noted that the expansion curve should be adapted to the brick body. Otherwise, due to inconsistent expansion, the bricks will separate from the mud, and even cause structural damage to the masonry. In order to eliminate and slow down the stress caused by the overall expansion of the masonry, it is necessary to reasonably consider the retention of the expansion joints of the masonry. In order to prevent excessive shrinkage of the mud during use, it is necessary to add an appropriate amount of expansion agent.

5 Other properties of fireclay cement
Thermal conductivity is an indicator of thermally insulating (or thermally conducting) refractory slurries. Generally, porous lightweight refractory clinker (or refractory clinker with high thermal conductivity) is used to replace general refractory clinker to reduce (or increase) its thermal conductivity. There is also a tendency to replace thermally insulating (or thermally conductive) refractory slurries with corresponding ordinary refractory slurries. As a buffer mud for masonry expansion joint filling material, its distinctive feature is that it has compressibility under high temperature load to buffer the expansion stress of masonry. Compression ratio is an important indicator of buffer mud. Because this kind of slurry has certain high temperature performance before and after compression, it is used in large blast furnaces, hot blast furnaces and coke ovens, and even on the working surface of blast furnaces.