Several incidents of early deterioration of structures have been reported in literature; such incidents have a negative impact. Insufficiencies in the durability design may result from a possible absence of explicit guidelines in design codes and standards that establish a standardized language for building design, construction, and operation. Most design codes and standards, while providing a robust framework for structural capacity and serviceability, do not address durability design to a desirable degree. This study examines and critically reviews the durability design in three international codes: the American, British, and Eurocodes. The study revealed that the European and British standards have comparatively more precise and comprehensive durability provisions, whereas the American code has a larger scope for development. The study introduces a proposal for the improvement of durability design provisions in codes to provide beneficial examples that can assist in the update of upcoming editions of these codes.

Inconsistencies in standards and codes result in confusion, increased costs, and do not promote the efficient use of concrete. In addition to inconsistencies, the lack of science-based approaches and data used for defining criteria in these standards and codes can limit the reliability and trust of these requirements. A review of industry documents indicates that inconsistencies and lack of science-based approaches exist across many documents, both throughout the industry and within ACI, relating to the corrosion of steel reinforcement embedded in concrete. This paper proposes to address five key issues to promote science-based standardization of requirements necessary for reinforced concrete systems exposed to corrosive conditions. These five issues include the need for: 1) standardization of chloride testing methods and requirements; 2) standardization of chloride reporting units; 3) standardization of terminology for specifying chlorides in cementitious systems; 4) standardization of exposure classifications for corrosive conditions; and 5) standardization of allowable chloride limits. This paper presents current inconsistencies in guide documents and codes for each of the items listed previously and then proposes an approach to standardize each using either available data and/ or a scientifically based approach. Recommendations for testing, reporting, definition of exposure classifications, and allowable chloride limits are then proposed. It is hoped that the systematic approach used herein will lead to standardization and consistency, less confusion, and will promote the efficient use of durable and economical concrete.

This research examines the performance of quality-controlled recycled concrete aggregates (QRAs) with fly-ash-based cement. Compared to concrete made from untreated recycled concrete aggregates (URC), quality-controlled recycled aggregate concrete (QRC) has superior physical, mechanical, and durability properties. Except for sorptivity, the physical, mechanical, and durability properties of QRC are almost identical to those of natural aggregate concrete (NC). The compressive strength, splitting tensile strength, flexural strength, fracture energy, and modulus of elasticity of QRC are higher than those of URC by 18.0%, 16.8%, 60.0%, 27.17%, and 43.46%, respectively. The abrasion resistance of QRC is approximately 60% higher than URC. Scanning electron microscope (SEM) image and energy-dispersive X-ray (EDX) analysis prove that quality control produces denser old interfacial transition zones (OITZ) with fewer microvoids. The QRA improves not only the pore structure but also the weak mortar structure attached to the aggregate. There is also a strong correlation between the compressive strength and splitting tensile strength, flexural strength, fracture energy, and modulus of elasticity of QRC. QRA can be used to compute the mixture proportions for concrete (certainly up to medium-strength concrete) according to either the Indian standard or the international standard. It is challenging to improve the sorptivity of recycled concrete aggregates closer to NC. In addition, QRC has an initial sorptivity of two times (initial) and a final sorptivity of 1.8 times higher than NC, whereas URC has an initial sorptivity of 3.5 times (initial) and a final sorptivity of 2.35 times higher than NC.

Biogenic sulfuric acid attack (BSA) is a biodegradation mechanism that causes accelerated deterioration of concrete sewer systems and wastewater treatment structures. BSA is a multi-stage biological process that deposits sulfuric acid over concrete surfaces. Due to its complex nature, there are no current standards to evaluate the presence, extent, and severity of BSA in concrete structures during service. The authors evaluated the chemical and biological conditions in an operational digester where BSA activity was suspected. The evaluation included microbial culture testing, quantitative polymerase chain reaction (qPCR) analysis of biofilm samples, pH measurements, and petrographic assessment of extracted samples. To evaluate the effect of oxygen on BSA activity, evaluations were performed in strictly anaerobic and oxygen-rich environments inside the same digester. The investigation determined that oxygen injection caused significant changes in the biological and chemical conditions inside the digester. The addition of oxygen promoted BSA activity and the associated production of sulfuric acid, and therefore accelerated concrete deterioration.

The use of three-dimensional (3-D) printing with cementitious materials is increasing in the construction industry. Limited information exists on the freezing-and-thawing (FT) performance of the 3-D-printed elements. A few studies have used standard FT testing procedures (ASTM C666) to assess the FT response; however, ASTM C666 is insensitive to anisotropy caused by printing directionality. This paper investigates the FT response of 3-D-printed cement paste elements using thermomechanical analysis (TMA) to examine the influence of directionality in comparison to cast counterparts. Cement paste with a water-cement ratio (w/c) of 0.275 was used. The critical degree of saturation (DOSCR) as well as the coefficient of thermal expansion (COTE) were determined for specimens with varying degrees of saturation (DOS). Micro-computed tomography (micro-CT) was conducted to quantitatively understand the heterogeneities in the pore microstructure of 3-D-printed materials. For the specimens fabricated in this study, the COTE and DOSCR are independent of the 3-D-printing directionality and were comparable to conventionally cast specimens. For samples at 100% saturation, the FT damage was higher in the 3-D-printed samples as compared to the cast samples. The use of a low w/c in the 3-D-printed materials, desired from a buildability perspective, led to low capillary porosity, which thus decreased the amount of freezable pore solution and increased the FT resistance of the 3-D-printed materials. Micro-CT analysis demonstrated a significant 4.6 times higher average porosity in the interfacial regions compared to the filament cores.