<p>Superabsorbent polymer (SAP)
hydrogel particles have been used as internal curing agents in concrete mixes
as they are capable of absorbing and subsequently releasing large amounts of
water. This reduces autogenous shrinkage during early stages of hydration. The
size, shape, and composition of the hydrogel particles can be controlled during
the synthesis, hence providing the opportunity to custom synthesize these internal
curing agents to elicit desired structure-property relationships. Utilization
of optimized dosage and formulation of SAP has the potential to improve the
microstructure, durability, and strength of internally cured concrete. </p>
<p>The first study focuses on the
synthesis and application of novel composite hydrogel particles as internal
curing agents in cementitious mixes. Composite polyacrylamide hydrogel
particles containing two different amorphous silica–either nanosilica or silica
fume–were used to investigate whether the internal curing performance of
hydrogel particles could be enhanced. The dosage and type of silica,
crosslinker amount were varied to identify the composite polyacrylamide
hydrogel particle composition that provides optimum benefits to internally
cured cementitious systems. The synthesized hydrogels were characterized by
means of absorption capacity tests, compositional and size analysis. The
beneficial impacts of the addition of composite hydrogels on cement paste
microstructure are highlighted, including the preferential formation of cement
hydration products (such as portlandite) within the hydrogel-induced voids that
appeared to be influenced by the composition of the hydrogel particles. The
interrelationship between extent of hydration, size of hydrogel voids, and
void-filling with hydration products was found to strongly influence mechanical
strength and is thus an important structure-property relationship to consider
when selecting hydrogels for internal curing purposes. This study informs the
design of composite hydrogel particles to optimize performance in cementitious
mixes. Additionally, it provides a novel means of incorporating other commonly
used admixtures in concrete without facing common challenges related to
dispersion and health hazards.</p>
<p>The second study focuses on the
utilization of two retarding admixture-citric acid and sucrose-to custom
synthesize composite polyacrylamides to investigate whether the composite
hydrogels could delay hydration of cement paste. Isothermal calorimetry
analysis results showed that composite sucrose-containing polyacrylamide
hydrogel particles were successfully able to retard main hydration peak of
cement paste, beyond the retardation capabilities of the pure polyacrylamide
hydrogels. Thus, this study provides avenues of exploring the utilization of
common admixtures to formulate novel composite hydrogels that imparts specific
properties to cementitious systems.</p>
<p>In another study, SAP formulated
by admixture industries were used to investigate the feasibility of internal
curing of bridge decks and pavement patches with SAP particles. The
microstructure and early age hydration properties of SAP-cured cementitious
systems were studied. Mitigation of microcracks in the matrix, along with
portlandite growth in SAP voids, were observed in SAP-cured mortars. Presence
of SAP also mitigated autogenous shrinkage and improved early age hydration as
observed by isothermal calorimetry analysis. This thesis highlights some of the
beneficial impacts of SAP-cured cementitious systems, and the potential to
harness those benefits in large-scale applications of SAP-cured concrete.</p>
<br>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/15070926 |
| Date | 29 July 2021 |
| Creators | Baishakhi Bose (11199993) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Improving_the_Performance_of_Superabsorbent_Polymers_as_Internal_Curing_Agents_in_Concrete_Effects_of_Novel_Composite_Hydrogels_on_Microstructure_and_Hydration_of_Cementitious_Systems/15070926 |
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