# A Durability Prediction Method for Historical Square Rebar Reinforced Concrete Buildings
###### Abstract  
Square rebars were developed and used for decades in the early development of reinforced concrete (RC) structures; however, the objectives of modern concrete structure durability analyses and standards are centered on round rebars in past decades, which are not suited for RC buildings utilizing square rebars. Considering the absence of proper evaluation techniques to evaluate the square rebar RC structures' durability accurately, a novel durability prediction method has been proposed for this type of historical building. The method is based on major parts as in-situ investigation, finite element model simulation, component importance analysis, and structural durability prediction. The durability prediction calculation method was established on the experimental results of the realistic historical concrete tests and corrosion-induced cover cracking experiments for square rebar components. It was found that the carbonization-resistant ability of historical concretes was relatively weaker than that of current concretes and the calculation method for critical corrosion depth of square rebar was different from that of round rebar. Furthermore, two typical application cases are presented to introduce the procedure of the method in detail. Consequently, the research outcomes can be directly used on the durability prediction and protection works for historical RC buildings. h +
Footnote †: journal: Applied Sciences  
12 November 2021  
10 December 2021  
**Problems:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The durability prediction method of the current China standard is structured on \"target service life\" which is dependent on the current durability design codes and current construction technology [18; 21]. However, a precise definition of \"target service life\" for historical RC structures has not been established in history; hence, the durability prediction relied on the current China standard cannot be employed directly. 2. Compared with the current level of the construction industry, the materials properties and construction techniques in history were backward [22]; thus, historical RC buildings cannot satisfy all of the current standards' durability design criteria. Accordingly, numerous elements and indexes from the current standards are inaccurate and unreliable for assessing the historical RC buildings. 3. The theoretical models and experiments in the standard [18] are all designed for round rebar components; however, according to the existing studies, the structural configuration design [23], the bond-slip behavior between rebar and concrete [24] and the rebar corrosion induced cracking model [25] for square rebar cases are very different from the round rebar cases. Due to the domination of round rebar for the current industry, the research on the historical RC buildings with square rebars is limited in number. [PERSON] and [PERSON] [17] studied the history of invention and development of steel rebar, contributing some unique pieces of information about vintage steel rebar. The book stated that the various section types of steel rebars in the early reinforcement industry were searching for the higher bond-slip strength between concrete and rebars, but it does not provide bond-slip strength between concretes and different types of rebars. [PERSON], [PERSON] and [PERSON] [26] tested material properties of square rebars on the abandoned members from the historical RC buildings (built between 1912 and 1949) in China. They reported that the square rebars were low-carbon and hot-rolled steel rebars, similar to the current round steel rebars, with an average yield strength of 278.60 MPa, and average tensile stress of 375.86 MPa. In another study, [PERSON] and [PERSON] [22] investigated the structural characteristics by testing the compressive strength of the old concretes from twelve historical RC buildings (built between 1912 and 1949) in China. The average compressive strength of the old concretes was 12-22 MPa.