PSI - Issue 67

Dan Huang et al. / Procedia Structural Integrity 67 (2025) 61–79 Huang, D., Velay-Lizancos, M., Olek, J./ Structural Integrity Procedia 00 (2024) 000–000

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3.3. Total permeable porosity and formation factor The total pore volume of concrete was determined following the procedure outlined in AASHTO TP135 ( AASHTO TP 135 - Standard Method of Test for Determining the Total Pore Volume in Hardened Concrete Using Vacuum Saturation , n.d.). This method involves determining the oven-dry mass ( A ), vacuum saturated mass ( B ), and apparent mass ( C ) of concrete disc samples (measuring 4 in. (100 mm) in diameter and 2 in. (50 mm) in height). The total volume of the permeable pores can then be computed using the following equation 1: ,% � � � � � � � � 100 (1) The assessment of concrete resistivity was conducted in accordance with AASHTO TP119-19 ( AASHTO TP 119 15(2019) | Techstreet Enterprise , n.d.), employing the uniaxial resistance test. This test utilized 4 in. x 8 in. (100 mm x 200 mm) concrete cylinders. The apparatus for uniaxial resistivity measurement comprised stainless-steel plate electrodes, electrical cables, a resistivity meter, and sponges saturated with lime. These sponges were positioned between the electrodes and the end surfaces of the concrete cylinders during testing. The resistance displayed by the resistivity meter during the test ( R measured ) is the actual bulk resistance (i.e., the resistance of the system composed of the concrete cylinder plus two sponges). To obtain the actual value of the concrete resistivity ( R cylinder ), the resistances of both the top and the bottom sponges ( R top sponge , R bottom sponge , respectively) need to be determined and subtracted from the bulk resistance ( R measured ) following the following formula given in Equation 2: �������� � �������� � ��� ������ � ������ ������ (2) The resistivity of the cylinder can be calculated using Equation 3: � �������� � � � (3) where is the resistivity of the cylinder, R cylinder is the resistance of the cylinder, A is the cross-sectional area of the cylinder, and L is the length of the cylinder. The formation factor was calculated following AASHTO PP84-19 ( AASHTO PP 84 - Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures , n.d.) using Equation 4: ��� � � � � (4) where, ��� is the formation factor that can be determined by dividing the resistivity determined by AASHTO TP119-19 ( AASHTO TP 119-15(2019) | Techstreet Enterprise , n.d.) by a pore solution resistivity � (0.127 Ωꞏ m). The resistivity of pore solution was estimated according to AASHTO PP84-19 ( AASHTO PP 84 - Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures , n.d.), by combining information on mixture proportions, chemistry of the cementitious materials and degree of hydration. The formation factor is an important indicator on the connectivity of pores in the concrete, and related the concrete durability (Qiao et al., 2019; Weiss et al., 2016). Concrete with a higher value of formation factor typically has less pore connectivity, less ingression of harmful chemicals, and thus better durability performance. As a side note, it should be pointed out that while AASHTO PP84-19 ( AASHTO PP 84 - Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures , n.d.) stipulated a test age of 91 days, in this study, to ensure consistency across all testing procedures, the resistivity of cylinders was determined at 28 days. 3.4. Water absorption The assessment of total water absorption and the absorption rate in concrete was conducted as per requirements of the ASTM C1585-20 (ASTM C1585, 2013), which involves testing of two concrete discs (measuring 4 in. (100 mm) in diameter and 2 in. (50 mm) in height). Prior to conducting the absorption test, the specimens need to be pre-