PSI - Issue 71

Garima Choudhary et al. / Procedia Structural Integrity 71 (2025) 424–429

426

The concrete mix design for M40 grade was formulated in accordance with IS 10262:2019 (BIS 2019), as summarized in Table 2. To evaluate the influence of gluconic acid on various properties, including setting time, workability, retention time, compressive strength, and rapid chloride permeability test, a series of tests were conducted. The specific mix proportions used for assessing setting time, workability, compressive strength and RCPT with gluconic acid are provided in Table 3. The setting time was determined in accordance with IS 4031 – 1988(2024) (BIS 2024), utilizing Vicat’s apparatus. Specifically, 300 grams of cement were mixed with 90 ml of water and the specified dose of GA, as outlined in Table 3, using a cement paste mixer. Workability was subsequently evaluated through the standard slump test as per IS 1199:1959(2018) (BIS 2018). The slump cone was methodically filled, compacted, and levelled in three layers, after which it was carefully lifted vertically to avoid disrupting the concrete structure. The resulting slump was recorded at 30-minute intervals until a zero slump was achieved, typically within 120 minutes. Following the workability assessment, cubic specimens measuring 150 mm x 150 mm x 150 mm were cast for the purpose of compressive strength testing. Compressive strength was evaluated at intervals of 3, 7, and 28 days. A total of 54 specimens were tested, with 9 samples designated for each dosage group, including a control group. For each dosage, 3 samples were tested at each specified age, and the mean compressive strength of the 3 samples at each testing interval was recorded as the representative strength. The Rapid Chloride Permeability Test (RCPT) was conducted per ASTM C1202 (ASTM 2019). Core samples (50 mm thick, 100 mm diameter) were vacuum-saturated and tested under 60V DC for 6 hours. The total charge passed, indicative of chloride permeability, was measured to evaluate the impact of gluconic acid on concrete durability.

Table 2. Concrete Mix Composition with Varying Gluconic Acid (GA) Dosages.

Binder (kg/m 3 )

Aggregates (kg/m 3 )

Water (kg/m 3 )

Mix

Cement

Fine aggregates

Coarse aggregates

Control 0.02% GA 0.04% GA 0.06% GA 0.08% GA 0.1% GA

420 420 420 420 420 420

880 880 880 880 880 880

1070 1070 1070 1070 1070 1070

160 160 160 160 160 160

Table 3. Mix Proportions and Admixture Dosages for Various Tests.

Dosage of GA (% weight of cement) 0.02, 0.04, 0.06, 0.08, 0.1 0.02, 0.04, 0.06, 0.08, 0.1 0.02, 0.04, 0.06, 0.08, 0.1 0.02, 0.04, 0.06, 0.08, 0.1

Dosage of PC (% weight of cement)

Specimen Type Cement Concrete Concrete Concrete

Property

w/c

Setting time Workability

0.3 0.38 0.38 0.38

-

0.06 0.06 0.06

Compressive strength

RCPT

4. Results and Discussions The setting times of cement paste incorporating gluconic acid (GA) at dosages ranging from 0.02% to 0.1% are presented in Fig.2. The incorporation of GA significantly extends both the initial setting time (IST) and final setting time (FST) of the cement. As the GA dosage increeses from 0% to 0.1%, the IST is observed to increase from 65 minutes to 170 minutes. Similarly, the FST is extended from 360 minutes to 550 minutes. These findings indicate that a GA dosage within the range of 0.06% to 0.1% can be effectively employed in concrete mixtures to achieve the desired prolongation of setting time, varying between 120 and 180 minutes. The workability of concrete is a critical factor in its transportation over long distances. Fig.3 illustrates the observed trends in workability with varying gluconic acid (GA) dosages ranging from 0.02% to 0.1%. The results show that GA exerts a significant influence on the workability of concrete. The control mix exhibits a gradual decrease in slump, from 300 mm to zero, within 90 minutes. However, with increasing GA dosages, slump values are sustained for a longer duration compared to the control mix. At a GA dosage of 0.1%, the slump decreases at a much slower rate, with workability retained for up to 180 minutes and a final slump value exceeding 150 mm. Fig.4 presents the retention time for a 120 mm slump (indicative of pumpable concrete) (ACI 2008) across different GA dosages. The results demonstrate a linear increase in the retention time of concrete with increasing GA dosages. Consequently, the addition of gluconic acid at higher dosages (0.08% to 0.1%) effectively prolongs the retention time of concrete to 180 minutes, while maintaining a slump value greater than 120 mm.