A revision of JIS A 5308 was officially announced in March 2019. This article explains the revision history and background of this standard, and the main revised content. In this revision, terms and definitions were newly defined and the item numbers were reviewed and the clause numbers were reordered. In addition, the use of sludge water using “stabilizer” for the purpose of environmental load reduction was newly defined. For high-strength concrete, the standard stipulates that the buyer can specify nominal strength in steps of 1（N/mm²）, and it adds 45 cm and 55 cm as new slump flow categories. Moreover, from the viewpoint of productivity improvement, concrete managed by slump flow was added to ordinary concrete, the slump categories were revised, the mixture plan format was changed, and the water-binder ratio description method was clarified.

The secondary lining concrete of a NATM tunnel is a difficult part of construction where the members are thin and concrete fills the enclosed space between the tunnel lining form and the ground. Owing also to the difficulty of construction, various deformations and malfunctions are sometimes found in the structures in use. In consideration of the above, various attempts have been made to improve the quality of new structures through application of the PDCA cycle, using methods to rationally evaluate the quality of the surface layer of lining concrete based on visual inspection. This report introduces cases of the analysis of the results of surface quality evaluation through visual inspection of the secondary lining concrete of some NATM tunnels built in the Tohoku region for the purpose of securing and improving quality.

In this paper, the phenomenon whereby fresh concrete undergoes significant loss of flowability when it is allowed to stand undisturbed for a while, which is a problem in construction work, is referred to as “stiffness”, and the stiffness generation mechanism is hypothesized based on microscope images of cement paste. The authors developed a chemical admixture (stiffness reducing agent) that suppresses the flocculation of cement particles and verified its effect through various tests. Through verification tests, we sought to quantify the degree of stiffness of concrete by a simple test called the vane shear test. Further, through various workability tests, we confirmed the possibility that stiffness may affect actual construction work, and we introduce construction cases where application of stiffness reducing agent improved filling performance in high density rebar areas and workability in lining work of fiber reinforced concrete.