The International Information Center for Geotechnical Engineers

Review of Polyurethane Resin Grouting for Rock Mass Stabilization

                                                                                                 

2.0 POLYURETHANE AS A CHECMICAL GROUTING MATERIAL

The broad category of polyurethane chemical grout has a number of applications to rock mechanics and civil engineering as a whole due to the wide range of strengths and chemical properties that are available. Concerning rock, applications range from water cutoff under dams and sealing water inflow in tunnels and mines, to structural support of rock for underground applications and rock slope stability. Because of the wide range of polyurethanes available, it is clear from the literature that there is some ambiguity in naming convention of these different types of PUR products, which generally causes confusion. Most research recognizes and separates polyurethane grouts based on their chemical and physical properties, however the names each category are given become interchanged amongst various sources. In describing the various types of polyurethane products for this report, as it will be necessary to separate my focus on PUR from the other types of polyurethane grout materials, I will describe and follow the conventions detailed below, from Arndt et al. (2008).

Single-stage polyurethane (PU) is the first category of polyurethane grout. PU is composed of only one component, and reacts with water to expand by the production of CO2 foam, and harden within rock fractures. PU products are typically described as hydrophilic, meaning they react with water both during and after the curing process, or hydrophobic, meaning they react with water only during the curing process (Bruce et al. 1999). Because PU rapidly expands to fill voids in the rock, it is predominantly used for sealing or water cutoff applications. Because its density and strength decrease significantly during its reaction with water, PU is not typically used for increasing the strength of rock masses (Arndt et al. 2008). The expansion properties of PU type materials is qualitatively demonstrated below in Figure 1.

PU expansion

Figure 1. PU Reaction with Water (Joyce 1992)

Polyurethane resin (PUR) is the second category of polyurethane grout, and the focus of this paper. PUR is composed of two stages of mixing, where the components react with each other to form the final product. PUR does not require water in the reaction process, but may still foam in the presence of water to a lesser extent than PU products. This typically helps infiltration of the PUR into rock fractures, however density and strength are reduced, although to a lesser extent than PU products. PUR products can attain much higher strengths than PU products, and are therefore used primarily for consolidating and increasing the strength of highly fractured rock masses (Arndt et al. 2008).

Epoxy is the third category of polyurethane grout. Epoxy, like PUR, is composed of two stages of mixing, however it is truly hydrophobic and will not react in the presence of water. Epoxy is typically used in structural foundations, where only a small quantity of product is needed. It is not typically used in rock mechanics applications (Arndt et al. 2008).

Table 1 describes the properties of the three types of polyurethane grout products.

Table 1. Comparison of Polyurethane Products (Arndt et al. 2008)

Comparison Table of PU Porducts 

This report will focus on the applications of PUR as described above. Note that in the literature, various forms of the abbreviations PU and PUR may be used interchangeably, however observing the number of mixing components, reactivity with water, and application setting (i.e. strength v. water cutoff) can resolve the true nature of the polyurethane product if there is any confusion.

 

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