A thermal conductivity prediction model of cement-based grouts for ground source heat pump

Cement-based material is frequently used in many aspects. For example, it is used as a sort of grout in a ground source heat pump system, whose heat conduction performance directly affects the heat change efficiency of the vertical ground heat exchanger. However, there are few thermal conductivity models applicable to cement-based grout materials, and the accuracy of published models needs to be improved. Therefore, a thermal conductivity prediction model for cement-based materials was performed according to the structure and heat conduction equation, which can predict the influence of many factors on thermal conductivity, such as aggregate content (sand-cement ratio), porosity and saturation degree. The overall accuracy is high, with 39 sets of data (75% of the data volume) whose errors are less than +/- 10%, meeting engineering applications, while the error using existing models mostly exceeds +/- 20%. This model can also predict a large proportioning range with the water-cement ratio from 0.3 to 0.7, the sand-cement ratio from 0.5 to 3.0, and the saturation degree from 0 to 1. Based on the model prediction results, the variation maps of different sand-cement ratios and porosity under dry and saturated conditions were proposed, and the simplified fitting formula for a range of common values was given.