Studies On Weathering And Durability Of Building Sealants

Building sealant is a kind of materials which are used in the joint of various construction joints, glazing glasses, sealing around windows and doors, playing the role of watertight and airtight, as well as energy saving and waterproofing, including sealants, caulks and pre-cast sealing materials. It is also a subfield of new type of building materials. When sealants are applying under the natural environment, weathering and degradation could happen due to the combination of factors of radiation, heat, oxygen, rain water, dusts and industrial pollution until they lose their function. Nowadays, higher requirements on building sealants have been given by modern architects. Thus, the key point of this paper is to study the durability and anti-weathering ability of sealants. The general research manner for weathering is to let materials experience natural exposure, or outdoor exposure, by exposing material to sunlight, temperature, humidity and oxygen, then evaluate its weathering ability via the changes on their performance. The accelerated weathering indoor may need to do to quicken a certain weathering factors. On one hand, it is for studying its aging mechanism. On the other, it is to imitate natural weathering.Experiments were done in 2 periods and 5 sets of building sealants were chosen in this paper for both natural exposure and accelerated weathering. For the first weathering experiment, the mild aging conditions, short aging time, 2000 hour, and two shapes of specimen were used. For the second, the aging time was prolonged to 5000 hour with higher heat aging temperature, 80℃and UV radiation with short wave length. Although the results of the second weathering experiment are mainly discussed in this paper for studying their aging mechanism, the data for the first weathering have been also reprocessed as a comparison.The emphasis of this paper is to give the manners that the durability among sealants can be evaluated. Firstly, introduce the way of Deviation coefficient. Compared with the previous way of Aging rate, the fluctuation of performances with aging time during weathering has been considered and has got the consistent conclusion with the real application. Then, summarize the trend of degradation of mechanical properties of sealants with aging time, and verify that the Utmost value does exist. Before it, the cross-linking reaction or merging of emulsion particles dominates and makes the mechanic properties increase gradually. After it, degradation would take over and induce the decrease on properties. Via Utmost value as a standard to evaluate the durability could not only get the conclusions which are as same as those in real site, but also have much understanding to the aging process than Deviation coefficient.It also shows that the sensitivity of sealants to factors of heat or radiation is different Some is more sensitive to heat, but some sensitive to radiation. The comparison and discussion have been made in this paper and their aging mechanism could be verified and explained by microstructure analysis. Finally the relativity of artificial weathering and natural exposure has been studied.