Synthetic Rubber’s Opportunities in the Construction Market

By Zhong Weike, CNCIC

Rubber materials are mainly used for waterproofing, seismic resistance and sealing purposes in buildings. Globally, the largest use of rubber materials in the construction area is waterproofing, followed by seismic resistance, and then sealing.

I. Rubber waterproof materials

To waterproof buildings is the most important aspect and the largest challenge in the construction field. Poor waterproofing in construction can cause repeated repairs and waste of water, and repairs may cost even larger than the expense of new construction. Asphalt is the cheapest waterproofing material. However, with the competition from new waterproof materials, fewer and fewer buildings use asphalt for waterproofing. Asphalt and SBS/APP modified asphalt materials accounted about 69.8% of China’s waterproofing materials market in 2004 (Source: China National Waterproof Building Materials Industry Association), while this ratio dropped to 41.2% in 2009. The latest data show that in 2011 the ratio was 37.6%. Among which, the use of SBS/APP modified asphalt waterproof rolls increased rapidly; its market share increased from 18% in 2004 to 25% in 2009, and then to 26.4% in 2011.
   The application of synthetic rubber in waterproofing is not limited in SBS modified asphalt. EPDM has also shown great potential in roofing and underground waterproofing systems, although its rapid growth has been hindered since 2008, probably because of its disadvantage in price compared to SBS modified asphalt, waterproof coatings and glass fiber modified asphalt shingles. Butyl rubber is used more often in underground waterproof. According to estimates, China’s consumption of waterproof rolls in 2010 included about 18 900 tons of EPDM and nearly 3 000 tons of butyl rubber. Besides, chlorinated polyethylene rubber, chlorosulfonated polyethylene and regenerated rubber can also be used in buildings as waterproofing materials.
   A rubber waterproofing coil is made from a layer of synthetic rubber by casting or extruding method, and then fixed to a building or structure by an adhesive to form a waterproof layer. Normally, the cost of rubber waterproofing is several times higher than that of the asphalt waterproofing. However, the rubber waterproof coil has been widely accepted by the construction industry due to excellent anti-leakage performance, good temperature and weather resistance and durability. Moreover, the density of the rubber waterproof materials, weighing less than 2 kg per square meter, is only 1/5 - 1/8 of the density of the asphalt roof waterproof layer. The lifetime of rubber waterproof materials is 5 to 10 times longer than that of traditional asphalt roof waterproof layer.
   EPDM rolls are generally added with some butyl rubber. Vulcanized EPDM rubber is the mainstream waterproof material. In recent years, EPDM waterproof roll is the only kind of rubber roll recommended to the construction industry by governments. It is applicable in roof and underground projects with grade I and grade II waterproofing standards.
   Rubber waterproof strips are mainly used as component joints in concrete structures, or as joints to resist expansion and contraction caused by temperature changes. Currently, most waterproof strips used in China are made from rubber, including natural rubber, chloroprene rubber, nitrile-butadiene rubber, butyl rubber, EPDM, rubber-modified PVC, blends of polypropylene and EPDM, etc. In addition, water swelling rubber is another waterproof material with high performance. It is normally made from water-soluble polyurethane prepolymer, acrylic water-absorption resin with natural rubber or neoprene.

II. Rubber supporting and seismic isolation materials

After a massive earthquake struck Sichuan in 2008, some researchers turned their attention to seismic isolation technology. However, the traditional design idea of rigid seismic isolation, i.e. “to overcome impact with rigidity”, still dominates. On the other hand, rubber seismic isolation technology and products lack publicity and are unfamiliar to most architecture designers. Thus, rubber seismic isolation is not very popular in China.
   The structural seismic isolation system uses a rubber seismic isolation bearing and has the properties such as bearing loading, seismic isolation, restoration and damping energy dissipation. It can reduce the seismic effects on the structure to ensure safety without significantly increasing building costs. Domestic data show that in an earthquake, the damage to the upper part of a structure with rubber seismic isolation bearing is only 1/4 to 1/8 of that in unisolated buildings. The main materials used in rubber bearing and seismic isolation include natural rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber and butyl rubber.
   The Earthquake Engineering Research & Test Center of Guangzhou University (EERTC) is a seismic test base designated by the Ministry of Construction of China which has influence at home and abroad. It set up a rubber bearings plant in Shantou of Guangdong in 1992, which was the first one of its kind to be developed in China. China Academy of Building Research (CABR) Certification Center is responsible for the certification of building seismic isolation devices. The existing relevant standards and regulations include “Code for seismic design of buildings” (GB50011-2001), "Rubber bearing” (GB20688.3-2006), “Technical specification for seismic-isolation with laminated rubber vibration isolators” (CECS126: 2001), etc.
   In addition to the plate composed of multi-layer rubber with various metal baffle and lead-stuffed cylindrical, rectangular solid or blocks, new pot type bearing, in which rubber itself acts as baffle, has been developed. It is made from high attenuation laminated rubber. The new composite bearing which uses chloroprene rubber, PTFE rubber to cover the surface of natural rubber, has resolved the durability problem. It is reported that the lifetime of such a bearing can be up to 100 years.
In recent years, the earth has entered a new era with frequent earthquakes. In order to improve seismic-resistance of buildings and structures, and to reduce the loss of life and property during earthquakes, it is imperative to expand production and application of the rubber support and seismic-resistant materials.

III. Rubber sealing materials

Building sealing materials include sealants, sealing strips, sealing gaskets, sealing expansion joints, etc.
   According to the statistics from the China Rubber Industry Association, China’s output of building sealing materials was 494 000 tons in 2009, up 9.7% yoy. Of which, the output of silicone sealants was 284 000 tons, up 9.2% yoy; the output of acrylic sealants was about 130 000 tons, up 8.3% yoy; the output of polysulfide sealants was 30 000 tons, up 11% yoy; the output of polyurethane sealants was 27 000 tons, up 22.7% yoy.
   Construction sealants, growing at a double digit annual rate worldwide, are mainly used for caulking. It is estimated that the global consumption of construction sealants is over 500 000 t/a. At present, construction sealants can be made from silicon rubber, modified silicone rubber, polysulfide rubber, modified polysulfide rubber, polyurethane rubber, acrylate rubber, butyl rubber, styrene butadiene rubber and so on.
   There are two types of building sealing strips: one is used for external glass walls in the structural part of a building; the other is used for inserting into the glass frameworks in the non-structural part of a building. It is estimated that the global consumption of building sealing strips is over 200 000 tons, among which synthetic rubber is most popular, accounting for 1/3 of the total consumption. Of which, chloroprene rubber leads, followed by EPDM and chlorosulfonated polyethylene rubber. In recent years, the use of high-end silicone rubber and thermoplastic elastomer has begun to increase.
   At present, the annual urban construction completed in China is over half billion square meters. This means that the market scale of windows and doors is more than 150 million square meters, among which aluminum alloy and plastic windows using sealing strips account about 80%, or 120 million square meters per year. The annual demand for sealing strips is 1.2 billion meters, and the demand for resin or rubber is about 96 000 tons. At present, almost all windows and doors use sealing materials made from PVC, while high quality EPDM has a disadvantage in price. In the future, with declining raw material costs, EPDM has a great opportunity to replace traditional sealing materials.