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Title: New generation of high performance cementitious materials : application of SAP in PC-GGBS matrices
Author: Almeida, Fernando do Couto Rosa
ISNI:       0000 0004 7655 5440
Awarding Body: Glasgow Caledonian University
Current Institution: Glasgow Caledonian University
Date of Award: 2018
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Construction industry is continuously searching for innovations and sustainable solutions to improve environmental, structural and cost requirements. The massive production of Portland cement (PC) demands high energy consumption, leads to significant emission of CO2 into the atmosphere, and requires large amounts of nonrenewable raw-materials. In an attempt to reduce its impact on the environment and improve sustainability and durability of cementitious materials, ground granulated blast furnace slag (GGBS), a by-product from iron and steel industries, is often used in concrete mixes. However, its addition leads to high cracking susceptibility of mortars caused by greater autogenous shrinkage triggered by self-desiccation processes. The lack of water and space for delayed GGBS hydration is also a critical issue in long term performance. In order to mitigate these negative effects, Superabsorbent polymers (SAP) can be used as internal curing agents. However, their effects on long term hydration and microstructure alteration are still unclear and deficient. Therefore, this research aimed to assess the compatibility and efficiency of SAPs in PC-GGBS matrices. Three types of SAP with different water absorption capacities, and four levels of GGBS substitution (0%, 25%, 50% and 75%) have been considered. The investigation searched to determine the effects of GGBS addition on SAP sorption behaviour, as well as, the influence of SAP on fresh and hardened state properties of PC-GGBS mortars (up to 180 days). The results proved the efficiency of SAP in providing water for internal curing; it reduces up to 90% of autogenous shrinkage, especially for high GGBS content. As a consequence, GGBS mortars are less susceptible to cracking formation. Addition of polymers results in pores with diameter greater than 2 pm for mortars with same water/binder ratio. However, SAP facilitates GGBS hydration (activated by portlandite) by supplying water and space (left by collapsed SAPs). Further C-S-H can be deposited into the smaller pores (under 20 nm of diameter) formed by high contents of GGBS. As a consequence, a relative late expansion of the hardened bulk volume is observed after the first week until the sixth week. SAP with alkalis crosslink up to 4.0wt% proved to be the most stable and suitable for both PC-GGBS cementitious systems. Above this limit, ion-exchanges between potassium/sodium (from polymer) and di- and trivalent ions (from GGBS) may take place, reducing SAP water-storage capacities. Ability of SAPs to re-fill pores with delayed GGBS products results in gain of strength over the time. Compressive strength of GGBS-SAP mortars is comparable to the reference samples at 180 days. In turn, creation of denser and poorly interconnected microstructures by SAP results in more durable cementitious matrices and hence more sustainable constructions
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available