Low clinker high performance concretes and their potential in CFRP-prestressed structural elements

Abstract

Three novel low-clinker-high-performance concretes (LCHPC) with clinker replacement levels of 54, 58 and 70 % were developed to substitute high-performance concrete (HPC) in carbon-fiber-reinforcedpolymer (CFRP) prestressed structural elements. The clinker substitution was achieved by a high amount of limestone filler and smaller amounts of metakaolin and silica fume. After 28 days, the LCHPCs reached high compressive strength values, between 77 MPa and 88 MPa, and Young's moduli between 35 GPa and 44 GPa. The LCHPCs showed self-compacting properties and low creep and shrinkage in comparison to a reference HPC. A finite element analysis (FEA) of the internal stress development over time in CFRP-prestressed structural elements was performed, including creep and shrinkage. A higher prestress level was maintained in the LCHPCs compared to the reference concrete, thanks to their low shrinkage and creep. In contrast, the use of ultra-high-modulus CFRP prestressing tendons leads to increased pre-stress losses.

Prestressing low clinker structural concrete elements by ultra-high modulus carbon fibre reinforced polymer tendons

“…New materials for prestressing of structural concrete elements, UHM-CFRP and LCHPCs introduced in 2016 [3] and 2019 [6] respectively, were tested to observe their behaviour during prestressing and during 4-point bending tests of such elements. In addition, the structural behaviour of these beams was further characterized.…”

“…This concrete recipe with a water to binder ratio (w/b) of 0.35, named C1, contained 443.0 kg/m 3 of ordinary Portland cement CEM I 52.5 R, 120.0 kg/m 3 fly ash, 20.0 kg/m 3 silica fume, 1107 kg/m 3 sand 0/4, 487 kg/ m 3 gravel 4/8 and 5.2 kg/m 3 superplasticizer (SP). This is the same recipe that was recently employed as a reference mix during the development of LCHPCs [6], based on a HPC used by the Swiss precast industry in CFRP prestressed structural elements [36]. In addition, to evaluate the potential of LCHPCs for prestressing applications, the recipe C4 (w/b = 0.17) was chosen from three recently developed LCHPCs [6].…”

“…This is the same recipe that was recently employed as a reference mix during the development of LCHPCs [6], based on a HPC used by the Swiss precast industry in CFRP prestressed structural elements [36]. In addition, to evaluate the potential of LCHPCs for prestressing applications, the recipe C4 (w/b = 0.17) was chosen from three recently developed LCHPCs [6]. In this recipe (now containing only 134.3 kg/m 3 of cement), large amounts of cement were substituted with 511.7 kg/m 3 limestone filler.…”

“…Ultra-high modulus (UHM) carbon fibre reinforced polymers have become recently more affordable with a cost of about 50 €/kg [3]. In addition, new guidelines [4,5] are allowing the development of novel low clinker high performance concretes (LCHPC) with clinker replacement levels of up to 70% [6]. The combination of both materials results in a very promising composite system that satisfies both the sustainability aspects and the technical improvement objectives.…”

Freeze-thaw resistance of blast furnace slag alkali activated mortars

“…However, excessive amount of energy need during production and causing high CO2 emission are among its disadvantages. Researchers state that it is responsible for 5-7% of the world's CO2, with around 0.66-0.82 kg CO2 emission per 1 kg of PC (Lämmlein et al, 2019;Peng et al, 2012;Xie et al, 2019;Zhang et al, 2018Zhang et al, , 2020 On the other hand, thanks to geopolymer material technology, it has been revealed that greenhouse gas emissions and energy consumption were reduced by 73% and 43%, respectively (Meyer, 2009). This makes it attractive to investigate geopolymer binders as an alternative binder instead of Portland cement in concrete production (Juenger et al, 2011).…”