Environmental and Economic Evaluation of Small-Scale Bridge Repair Using Cross-Laminated Timber Floor Slabs

Abstract

Cross-laminated timber (CLT) has gained popularity worldwide in recent years, and its use in buildings and civil engineering structures has attracted attention in Japan. In this study, the life-cycle greenhouse gas (GHG) balance and costs associated with CLT floor slabs were evaluated with respect to small-scale bridge repair as the first instance of the use of CLT in civil engineering projects in Japan. Additionally, waterproofing treatment was applied to CLT slabs, and the potential GHG and cost reduction of CLT in comparison with reinforced concrete (RC) slabs were examined. GHG emissions were the smallest for non-waterproofed CLT slabs and the greatest for RC slabs. When replacing RC slabs with CLT slabs without waterproofing, fossil-derived GHG emissions can be reduced by 73 kg-CO2eq/m2 per slab, and fossil/wood-derived GHG emissions can be reduced by 67 kg-CO2eq/m2; however, the use of disposed CLT as fuel is essential. Moreover, a reduction in GHG emissions can be expected if RC slabs are replaced with CLT slabs that are waterproofed only once every 20 years. Further, the cost associated with RC slabs is 20% of that attributable to CLT slabs. Hence, measures need to be taken to reduce the cost of CLT and waterproofing materials.

Life Cycle Regional Economic Impacts of Bridge Repair Using Cross-Laminated Timber Floor Slabs: A Case Study in Akita Prefecture, Japan

“…Iwase et al [23] reported that the cost of using CLT is higher than that of RC in the life cycle of floor slabs; however, this study shows that the regional economic impact is larger with CLT. It has also been shown that the regional economic impact of NWP CLT is significant.…”

“…Therefore, not only the costs borne by the consumer but also the regional economic impact must be evaluated. However, this aspect has not been considered in previous studies [22,23]. Conversely, other previous studies [24][25][26] have shown that, despite its associated high construction costs, the use of timber has a positive impact on the regional economy for timber check dams [24,25] and high-rise mass timber buildings [26].…”

“…This study targeted the repair of a 10-m-long and 3.3-m-wide girder bridge in Daisen City, Akita Prefecture, Japan, constructed in 1990 and managed by Akita Prefecture itself [23]. Before the repair, timber floor slabs with a simple structure consisting of square timber (chestnut) lined up perpendicular to the bridge axis were used.…”

“…According to Ahmed and Arocho [22], the construction of mass timber buildings primarily with CLT is more expensive than concrete. According to Iwase et al [23], when CLT is used for floor slabs, the overall cost of construction, maintenance, and disposal for the consumer are higher than that of reinforced concrete (RC). CLT floor slabs involve various industries throughout their life cycle, including manufacturing, use, and disposal.…”

“…In this study, we quantitatively evaluated the regional economic impacts of bridge repair using the CLT floor slabs studied by Iwase et al [23] during their overall life cycle from construction to disposal by estimating the future input-output tables using past-topresent input-output tables. In addition, CLT floor slabs with and without waterproofing were also considered.…”