Lat et al. / Malaysian Journal of Fundamental and Applied Sciences Vol. 16, No. 1 (2020) 70-74 70 A review of polyurethane as a ground improvement method Diana Che Lat a, c,* , Nazri Ali c , Ismacahyadi Bagus Mohamed Jais b , Nor Zurairahetty Mohd Yunus c , Roslizayati Razali a , Adrina Rosseira Abu Talip a a Faculty of Civil Engineering, Universiti Teknologi MARA Johor, Pasir Gudang Campus, 81750 Johor, Malaysia. b Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia. c Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia. * Corresponding author: dianacl@johor.uitm.edu.my Article history Received 10 July 2018 Revised 2 May 2019 Accepted 3 July 2019 Published Online 2 February 2020 Abstract Ground improvement based on lightweight materials is commonly applied as a method to overcome the problem related to excessive and differential settlement. The application of polyurethane (PU) as a ground improvement work currently increases in demand due to its well performance in many ground improvement projects. The properties and strength of different types of PU available in the market, together with the safety issues and precautions are highlighted in this paper. Due to its lightweight properties, buoyancy behavior of the lightweight foam often causes uplift which jeopardize the stability of the existing structure. Since it is applied in the ground, awareness on PU degradation needs to be emphasized. The suitability and applications of PU as one of alternative method for ground improvement works are also highlighted in this paper. Keywords: Polyurethane, lightweight, buoyancy, ground improvement © 2020 Penerbit UTM Press. All rights reserved INTRODUCTION Excessive soil settlement has caused many instabilities of soil foundation for structure construction. To ensure the stability of structure constructed on soft soil, ground improvement is very crucial to be executed. However, inadequate ground improvement during pre- construction works commonly lead to post-construction failure of the soil foundation. Rapid remedial work is required to mitigate the failed foundation thus prevent further deterioration of the soil foundation. Amongst the available conventional ground improvement methods in the market, the emphasize is on the lightweight material in order to minimize additional load impose to the poor soil foundation. The remedial work under consideration should not cause major disruption to the existing structure. Therefore, ground improvement using polyurethane (PU) seems to be the most efficient method as a remedial work. Thus, this study is carried out in order to review the properties, strength, applications, and suitability of PU as a ground improvement method. Chemical properties and composition of PU Production and investigation of PU was initiated by Dr. Otto Bayer in 1937 (Howard, 2012). PU is a class of polymer which exhibits a wide range of mechanical properties (Hepburn, 1992). It is a mix of polyol (- OH) and isocynate (-NCO) which react at two major reactions occurred during polymerization of PU (Bayer, 1947; Buzzi et al., 2008; Badri, 2012). Isocyanate that reacts with water will disubstituted with urea and generates carbon dioxide. This process is known as blowing reaction because the carbon dioxide is acting as an auxiliary-blowing agent. Reaction also occurs between the polyfunctional alcohol (polyol) and the isocyanate ratio. It generates a urethane linkage in a reaction referred to as the gelation reaction. The isocyanate reacts slowly with alcohols, water, and the unstable amino products without the presence of catalyst. The reaction between polyol and isocynate is as follows (Badri, 2012): R-N=C=O + R’-O-H → R-NH-C(O)-O-R (1) Isocyanate + Polyol → Polyurethane There are two types of polyol which are polyester and polyether polyols. Polyester polyols are generally consisting of adipic acid, phthalic anhydride, dimer acid (dimerized linoleic acid), monomeric glycol, and triol. Polyester polyols have low acid number (normally 1– 4 mg KOH/g) and low moisture content (less than 0.1 %). These properties are not easily achieved unless a high-technology processing method is applied. Polyester polyols are usually supplied at higher price compared to polyether polyols. Polyether polyols on the other hand are commercially produced from catalytic reaction of alkylene oxide i.e. propylene oxide or ethylene oxide to di- or polyfunctional alcohol (Badri, 2012). Diisocyanates are a family of chemical building blocks used to make a wide range of PU products. The most widely used aromatic diisocyanates are toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). Less widely used, but still important, are the aliphatic diisocyanates, including hexamethylene diisocyanate (HDI), hydrogenated MDI (H12MDI), and isophorone diisocyanate (IPDI). Exposure to uncured diisocyanates may cause certain health effects, however, consumer exposures to uncured isocyanates are expected to be of very low magnitude and frequency. Consumer products containing uncured isocyanates (such as certain adhesives and sealants) are accompanied by product safety information like warning labels that include the characteristics of the chemicals, their approximate cure time, and how consumers can properly protect themselves while handling the product. However, fully reacted PU polymer is chemically inert (Dernehl, 1966). Because of the flammability of the material, it has to be treated with flame retardants, almost all of which are considered harmful (United States Environmental Protection Agency, 2014). Due to the severe toxicity of isocynate, some researches have been undertaken to minimize the use of isocyanates to synthesize PUs. Non-isocyanate-based PUs (NIPUs) have recently been developed REVIEW ARTICLE