PSI - Issue 70

Surya Mouli R. et al. / Procedia Structural Integrity 70 (2025) 239–246

241

Table 1. Typical Properties of Corn and Tapioca Starch Property

Corn Starch

Tapioca Starch

Appearance

Fine white powder Fine white powder

Particle Size (µm)

15

10

Gelatinization Temperature (°C) Water Absorption Capacity

60 – 70

55 – 65

High

Very High

pH (1% solution)

6.8

6.5

2.1 Starch Gel Preparation for Internal Curing

This research utilized starch gel obtained from corn and tapioca starch to develop bio-based internal curing agents. The laboratory weighed dry starch as a required percentage of cement weight before the mixture operation began. The starch was then combined with water at a 1:10 by weight ratio. To induce gelatinization, the mixture was heated to about 85-90°C while stirring continuously. The starch solution obtained a homogeneous viscous state from gelatinization before being allowed to cool down to reach room temperature. The produced gel was added to the concrete mix by partially substituting the batch water, ensuring that the total water content remained constant. Partially substituting batch water with the gel enabled effective hydration water supply which led to lower autogenous shrinkage while enhancing the concrete's microstructure in its hardened state. IS 10262:2019 specifies concrete mix proportions for M40 grade. The control mix (CM) has no internal curing agents. Other mixtures include corn and tapioca starch at various proportions (0.5 to 2%) by weight of cement. Each mix contained a consistent relation of water to cement measured at 0.40. The mix proportions of both CS and TS mixes are listed in Table.2. 2.3 Mixing and Casting Procedure A pan mixer performed the mix sequence where cement and aggregates dry mixed for two minutes followed by water with gel addition along with starch gel mixing for another three minutes. Specimens were demoulded for 24 hours and submerged in water at 27±2°C for curing before examination. 2.2 Mix Proportioning

Table 2. Mix Proportions with Internal Curing Agents Mix ID Starch Gel (%)

Starch Gel Water Adjusted Mix Water

Cement

Fine Aggregate

Coarse Aggregate

(kg/m³)

CM

0.00

0.00 2.10 3.15 4.20 5.25 6.30 7.35 8.40

0.00

168.0 147.0 136.5 126.0 115.5 105.0 94.5 84.0

420 420 420 420 420 420 420 420

660 660 660 660 660 660 660 660

1165 1165 1165 1165 1165 1165 1165 1165

CS-0.5 / TS-0.5 0.50 CS-0.75 / TS 0.75 0.75 CS-1.0 / TS-1.0 1.00 CS-1.25 / TS-1.25 1.25

21.00 31.50 42.00 52.50 63.00 73.50 84.00

CS-1.5 /TS-1.5

1.50

CS-1.75 /TS-1.75 1.75

CS-2.0 /TS-2.0

2.00

3. Testing methods Testing adhered to all applicable standards mentioned in the relevant codes. The workability characteristics of fresh concrete were determined through the slump test procedure according to IS 1199:2018. The compaction factor test functioned to check the mix's consistency as a separate test requirement. The testing method for compressive strength