Spatiotemporal variations in power grid carbon intensity and their impact on steel fiber-reinforced concrete emissions

China's energy transition has created unprecedented spatiotemporal heterogeneity in power grid carbon intensity, yet conventional life cycle assessment methodologies using national averages potentially misrepresent emissions for electricity-intensive products. This study develops a spatiotemporally explicit framework using steel fiber production to examine these impacts. Analysis of 31 provinces reveals 24-fold spatial variation (0.04-0.97 kg CO₂e/kWh), with steel fiber emissions ranging from 0.72-4.35 kg CO₂e/kg. Conventional methods misrepresent emissions by up to 177% in clean regions, masking reduction opportunities. Under the adopted average-grid accounting framework, 87.5% of the 465 potentially beneficial directional routes remain carbon-beneficial after accounting for actual transportation distance, while 37% show calculated emission reductions of 0.6–2.4 kg CO₂e/kg. Under the adopted quarterly production allocation scheme, temporal scheduling in hydropower-dominated regions yields calculated emission reductions of up to 5.40%, without requiring changes to production equipment or technology. These findings reveal fundamental limitations in current carbon accounting and provide a screening-level framework for low-carbon procurement and industrial planning.