Valorization of dredged sediments in self-consolidating concrete: Fresh, hardened, and microstructural properties

Highlights

• Up to 20% cement replacement, eco-SCC was fabricated with adequate fresh properties.

• Equivalent strengths were found up to 20% of cement replacement by sediments.

• Composite binder showed slower hydration kinetics than the conventional binder.

• Pozzolanic reactivity of sediments reduced the micro-pores and densified the ITZ.

• Sediments could be used as SCMs to reduce the CO₂ footprint of SCC.

Abstract

Several studies have proven the use of dredged sediments as supplementary cementitious materials (SCMs), but limited information is available on the effect of such treated sediments on self-consolidating concrete performance. The main objective of this study was to evaluate the performance of self-consolidating concrete (SCC) fabricated with treated sediments. The sediments were thermally treated at 800 °C for 1 h. The packing density of the granular skeleton was optimized to reduce the paste content and produce SCC with relatively low binder content. Three different SCC mixtures were prepared with 0%, 10%, and 20% cement replaced with treated sediments by mass. Key fresh, physical, hardened, and microstructural properties of the investigated SCC mixtures subject to different curing regimes were evaluated. The test results showed that the optimized SCC mixtures exhibited adequate self-consolidation characteristics. The particle size and high chemical activity of the sediments led to pore refinement of micro-pores, increased density, improved microstructure, and reduced micro-cracks of the investigated SCC mixtures. Furthermore, the use of up to 20% of treated sediments resulted in a compressive strength of 66 ± 1 MPa at 91 days, which is comparable to that of the reference mixture made without any sediments. Leaching test results confirmed the ecological potential of producing SCCs based on sediments, which could be an interesting alternative of using local materials to reduce the high demand of cement, thus further reducing the CO₂ footprint of concrete structures.

Introduction

Self-consolidating concrete (SCC) can be used to facilitate concrete mixing and placement and ensure proper filling of complex frameworks without any mechanical consolidation. This can help reduce cost, labor, and construction time and provide more freedom in the design and enhancement of surface finish (Khayat et al., 1999). The design of stable SCCs can enhance the interfacial transitional zone (ITZ) properties with embedded reinforcement and with aggregates that can lead to greater SCC performance (Khayat et al., 1999). One of the drawbacks of SCC is its higher content of fine powder attributed to the relatively high-binder content than that in conventional concrete. Extensive research has been conducted on the feasibility of valorizing abundantly available by-products as supplementary cementitious materials (SCMs) to partially replace cement and reduce the environmental footprint of SCC. Commonly used SCMs are fly ash, ground-granulated blast-furnace slag, silica fume, limestone filler, marble powder, calcined clay, palm oil fuel ash (Mohammadhosseini et al., 2015), and waste ceramic nanoparticles (Lim et al., 2018). These materials are primarily composed of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and calcium oxide (CaO). The presence of additional oxides can be beneficial to produce additional pozzolanic calcium-silicate-hydrate (C–S–H) gel.

Significant volumes (more than one billion cubic meter) of dredged sediments are produced worldwide every year (Benzerzour et al., 2017). These materials are stored or disposed at sea when they are not contaminated. However, these sediments are very heterogenous: the provenance and dredging time during the year have a crucial influence on their composition. This makes each sediment a unique material which requires special treatment. The valorizing of dredged sediments in concrete, engineered materials, and civil engineering applications presents considerable benefits. Such valorization includes the fabrication of bricks (Samara et al., 2009), ceramic products (Xu et al., 2014), lightweight aggregates (Liu et al., 2018), and road construction materials (Kasmi et al., 2017). Recent studies have demonstrated that thermally treated sediments can render the sediments more reactive and that treated sediments can be useful for clinker production (Aouad et al., 2012; Faure et al., 2017) or as SCM.

Dang et al. (2013) designed a new blended cement containing 8%, 16%, and 33% of treated sediments from the trap Lyvet on the Rance River in France. The sediments were heated at 650 °C and at 850 °C for 5 h. Blended cements containing 8% treated sediments secured equivalent long-term compressive strength compared with the reference mixture made without any sediment. The authors reported that the composite binder required a longer curing period for the development of mechanical properties. Ez-zaki and Diouri (2019) investigated the microstructural and physic-mechanical properties of mortars made with 8% and 33% thermally treated sediments and shell powder at 650 and 850 °C for 5 h. Despite the pozzolanic reactivity of treated sediments, the compressive strength of the mixtures containing the treated sediment was lower than that of the control mortar. Van Bunderen et al. (2019, 2017) studied the early-age hydration and autogenous deformation of cement paste containing 20%, 30%, and 40% of flash calcined dredging sediments treated at 865 °C. The treated sediments and fly ash developed a similar early-age hydration behavior, and the addition of sediments reduced the autogenous shrinkage of mortar. Snellings et al. (2017, 2016) studied the pozzolanic reactivity of flash calcined sediments (from the port of Antwerp, Belgium) treated at temperatures of 820, 865, and 905 °C. The pozzolanic reactivity of sediments was found to be inferior to that of metakaolin but was superior of that of siliceous fly ash in a calorimetry based pozzolanic reactivity test. Zhao et al. (2018) investigated the effect of using 10%, 20%, and 30% cement replacement of uncontaminated sediments on properties of mortar and concrete mixtures. The reported results showed that dried and finely ground sediments can be used as partial substitutes of cement by up to 20% without hindering the mechanical properties of the mixtures. Benzerzour et al. (2018, 2017) developed a new blended cement containing 8% and 15% sediments thermally treated at temperatures of 650, 750, and 850 °C for different durations ranging between 1 and 3 h. Test results showed that mortar mixtures incorporating 15% sediments treated at 850 °C for 1 h developed better mechanical strength than the control mortar.

Although various non-traditional by-products have been recycled to SCC, such as waste carpet fibers and palm oil fuel ash (Mohammadhosseini et al., 2018, 2017), limited research has been conducted on the engineering properties of SCC incorporating the treated sediments. Sediments used as fillers in SCC achieved good performance (Rozas et al., 2015; Rozière et al., 2015). Bouhamou et al. (2016) evaluated the influence of using 10%, 15%, and 20% replacements of cement by calcined dam mud sediments treated at 750 °C for 5 h on the shrinkage of SCC. They reported that the increase in calcined mud content resulted in more viscous and less workable SCC for a given water content. A higher mechanical strength of SCC containing 10% calcined mud was reported. However, notably, the control SCC mixture exhibited the highest strength development. It was also reported that the addition of calcined mud resulted in lower autogenous shrinkage. This was attributed to the formation of expansive calcium aluminate hydrates, which compensated for the shrinkage. Nevertheless, the effect of sediments on fresh, hardened, and microstructural properties of SCC are still not well understood.