This study investigated the shrinkage properties of concretes using blast furnace slag cement and frostresistant accelerator as a construction technology in environmental-load-reducing cold weather concretes. The investigation results showed that as the frost-resistant accelerator was added to both Ordinary Portland Cement (OPC) and Blast Furnace Slag Cement (BB), the effect on the properties of fresh concrete was reduced and the compressive strength was increased from an early age. In addition, the free shrinkage strain and cracking potential at the same age tended to increase and the study result verified that the crack generation was also fast in the restrained condition. Meanwhile, the study results verified that the length of both of OPC and BB tended to increase upon adding the frost-resistant accelerator. Pore volume <30 nm diameter, in particular, 20–۳۰ nm pore volume, and ink-bottle pore volume decreased such that the shrinkage volume increased, and the change in pore volume in this range was regarded as having a large effect on the shrinkage properties.

Introduction

The use of blast furnace slag cements has been expanded to reduce environmental load or employ industrial wastes efficiently. More recently, low heat and shrinkage-reduced blast furnace cement, which has a high content ratio of blast furnace slag, and Energy CO2 Minimum (ECM) cements that achieve the Class C slag content ratio have been studied, but their use has been limited practically [1–۳]. Although blast furnace slag cements have many advantages such as low heat, increased long-term strength, flame interruption performance, and suppression of the alkali–aggregate reaction, they also have drawbacks such as delayed early strength development and early frost damage during winter construction due to high temperature dependence, which is why much care must be taken when using blast furnace slag [4]. When concretes are used in winter, it is important that the concretes do not freeze until sufficient strength has been developed to prevent early frost damage due to the delayed strength development or freezing, and heat curing via temporary enclosure and use of a heater is typical [5–۸]. However, the use of a temporary enclosure for concrete curing may cause CO2 emissions due to the heater or warm curing in a space with extremely bad heat efficiency, which is why the use of a frost-resistant accelerator has increased to prevent early frost damage [9–۱۴].