PSI - Issue 64

Sothyrak Rath et al. / Procedia Structural Integrity 64 (2024) 122–129 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Mixing ratios and curing conditions used for the samples. Series w/c AEA (wt%) * Unit content (kg/m 3 ) Cement Water Sand Gravel

Admixtures (g/m 3 )

Curing

Air content (vol%)

SP

TH

AF

AEA

0.3 0.4 0.5 0.6 0.7 0.5

– – – – – 0

416 364 323 290 262 323

125 146 161 174 184 161

792 792 792 792 792 792

1042 1042 1042 1042 1042 1042

4161.2 2913.9

– – –

– – –

– – – – – –

Air or Water (for 28 days)

2.00 6.00 1.75 3.50 3.80 1.75 3.25 7.00

S1

– – – – – –

3475.5 5510.3

17.4 27.6

S2

– – –

– – –

Water (for 28 days)

0.002 0.006

6.5

19.4

* Ratio used in the cement mix

was collected from more than ten holes at a depth of 10 mm. These parameters were selected to minimize the effects of bleeding, segregation, and surface defects on the powder properties and to determine the average powder porosities of the samples. After collection, the powder was sifted using a 106-µm sieve to remove larger particles that could have fallen off the specimen during drilling. The powder was then D-dried for 24 h and stored in an enclosed glass bottle until further use. As discussed earlier, the pore structure properties (e.g., porosity) of the cement paste are important for assessing frost resistance. However, the porosity of the collected powder is a combination of that of the cement paste and the aggregates. Therefore, it was necessary to separate these porosities, which was done through an acid-treatment process. Methanolic maleic acid was used to remove cement from the concrete powder with probable inaccuracies of <2% for the total cement content remaining and <7% for the partially dissolved total aggregate content (Clemeña (1972)). Owing to the high accuracy of this method, this study adopted this acid solution to evaluate the aggregate porosity using the following process. First, 20 ml of a 20% methanolic maleic acid solution was prepared using maleic acid (99.0%, lab grade; Wako Pure Chemical Industries, Osaka, Japan) and anhydrous methanol (99.5%, Wako 1 st grade; Fujifilm Wako Pure Chemical Corporation, Osaka, Japan). Next, 0.5 ± 0.1 g of concrete powder was added to this solution and stirred with a magnetic stirrer at 20 °C at a rotational speed of 500 rpm for 15 min. The remaining aggregate powder was then collected via vacuum filtration with a minimum holding particle size of 5 μ m. After that, the powder was oven-dried at 40 °C for 24 h. The powder porosity was measured through mercury intrusion porosimetry (MIP) (PoreMaster-60GT; Anton Paar, Graz, Austria). The pressure applied in this method was converted to the pore diameter using the Washburn equation (Washburn (1921)). We used 0.480 N/m for mercury surface tension (ISO 15901-1:2016 (2016)) and a 140° contact angle between the pore wall and mercury (Sakai et al. (2014)) in this equation. To perform MIP on the powder sample, we used a capsule (Fig. 1(a)) with four holes at the top to prevent the powder from being sucked into the machine. The total concrete and aggregate powder porosities were measured via MIP from the 0.5 ± 0.1 g concrete powder and aggregate powder (remaining after acid treatment), respectively. Then, Eq. (1) was used to calculate the paste porosity within the pore diameter range of 10 – 250 nm, which was employed to eliminate the influence of gaps between the powder particles on the powder porosity (Tanaka and Sakai (2021)).

(1)

where Φ p (ml/ml), Φ c (ml/ml) and Φ a (ml/ml) are the porosities of the paste, concrete, and aggregate powder, respectively, and V c (ml) and V a (ml) are their respective volumes.