Alkali-activated slag (AAS) binders offer a sustainable alternative to Portland cement, yet their long-term mechanical properties remain uncertain. Despite reported declines in strength and stiffness over time, the mechanisms behind these reductions are not fully understood. Existing research largely focuses on short-term properties or isolated factors, and there is a lack of integrated studies spanning paste, mortar, and concrete. The role of dry shrinkage in longterm degradation and the development of effective mitigation strategies has also received limited attention.
This thesis addresses these gaps by investigating the causes of long-term reductions in the strength and elastic modulus of AAS mortars and concretes and evaluating potential solutions. An experimental program examined the influence of activator type (sodium silicate vs. sodium carbonate), curing regime (ambient, 7-day fog, and fog–sealed curing), and gypsum addition. Mortar and concrete specimens were monitored for their compressive strength, flexural strength, elastic modulus, and dry shrinkage over a six-month period. Results were also compared to traditional Portland cement systems (CEM I and CEM III) to benchmark performance. Moreover, correlations between mechanical properties and dry shrinkage were analysed, and the elastic modulus and shrinkage were compared with model predictions. Findings indicate that early fog curing substantially reduces shrinkage and increases mechanical properties by limiting moisture loss and microcrack formation. Sodium silicate activation produces denser microstructures, higher strengths, and stiffness than sodium carbonate systems. Incorporating 6% gypsum mitigates shrinkage by over 30% through ettringite formation and pore refinement, while slightly delaying early strength gain.
In AAS mortars and concrete, increasing dry shrinkage reduces both elastic modulus and flexural strength, while compressive strength may still rise under ambient curing, whereas Portland cement mortars (CEM I and CEM III) exhibit simultaneous gains in compressive strength, elastic modulus, and flexural strength due to ongoing hydration, and early-age fog curing in AAS mitigates shrinkage and microcracking, maintaining higher stiffness and flexural strength with long-term stabilisation as the microstructure densifies. Comparisons with Standard predictive models indicate that OPC-based codes overestimate the AAS elastic modulus, although long-term shrinkage trends are reasonably captured.
This study provides new insight into the mechanisms linking shrinkage to long-term degradation in AAS and demonstrates that combining sodium silicate activation, gypsum addition, and early fog curing offers a practical route to durable, shrinkage-resistant, and sustainable AAS concretes suitable for structural applications. ... Read more

Timber–Concrete Composite (TCC) floor systems offer a sustainable and structurally efficient solution by combining the tension capacity of timber with the compressive strength of concrete. Despite their advantages, the environmental impact of concrete and conventional steel reinforcement remains a concern. This thesis explores the use of alternative reinforcement methods and materials, focusing on loose basalt fibres, to evaluate their mechanical and environmental performance in TCC slabs.

The central research question is: “What are the mechanical and environmental implications of using a suitable alternative reinforcement method and material in timber-concrete-composite (TCC) floor systems, assessed against a case study?”

A standard floor element from the DPG Media building was selected as the case study. Eight reinforcement alternatives were evaluated through a multi-criteria analysis (MCA), considering parameters such as strength, ductility, sustainability, and buildability. The most promising option, loose basalt fibre reinforcement, was selected for further comparison against the original steel mesh-reinforced design.

In the MCA, each reinforcement alternative was scored from 0.0 to 100.0 per criterion, with scores linearly interpolated between the best and worst performers. To reflect the priorities of this study, environmental impact was weighted twice as heavily as performance capability, which itself was weighted four times more heavy than buildability and cost. The final weights assigned were: sustainability (0.5), performance capability (1.0), and buildability and cost (each 0.125). Performance capability included two equally weighted sub-criteria, ensuring it did not disproportionately influence the overall outcome. The total score for each alternative was calculated by multiplying the criterion weights with the respective scores and summing the results.

To test the robustness of the MCA outcome, a sensitivity analysis was performed on both the weighting scheme and scoring method. This confirmed that the selection of basalt fibre reinforcement remained consistently high across variations, reinforcing confidence in the methodology and its conclusions.

Numerical modelling was conducted to assess crack formation due to shrinkage (using LS-DYNA) and structural capacity under horizontal wind loading (using GSA Oasys) for the selected reinforcement alternative. LS-DYNA models were developed for three scenarios: non-reinforced, steel mesh-reinforced, and basalt fibre-reinforced slabs. A smeared cracking approach was used to estimate crack widths under expected shrinkage. The slab was supported with pinned edges and discrete spring elements representing the stiffness of notched connections with dowels. The steel mesh model was validated against the Eurocode analytical method, yielding a crack width of 0.19 mm, which complies with the Eurocode’s Serviceability Limit State (SLS) requirements of 0.40 mm. These limits are primarily based
on corrosion prevention. For basalt fibre, which is corrosion-resistant, a maximum crack width of 0.70 mm was adopted based on aesthetic considerations found in literature. The model results exceeded both analytical predictions and crack width limits:
• Non-reinforced slab: 0.95 mm
• Basalt fibre-reinforced slab: 0.96 mm
• Steel mesh-reinforced slab: 1.35 mm

A separate GSA model was developed to assess stress distribution in the top concrete layer of the TCC slab under horizontal loading, comparing standard steel mesh and basalt fibre reinforcement. For extra validation, the values are also compared to the values from the SCIA-model from the documentation of the original design. The unity check for steel mesh was 0.55 in the GSA model and 1.0 in the SCIA model. For basalt fibre, an additional safety factor was applied due to its brittle nature, resulting in unity checks of 0.31 (GSA) and 0.43 (SCIA). These results demonstrate the superior mechanical performance of basalt fibre, supporting the MCA-based material selection.

Environmental impact was assessed using a cradle-to-gate Global Warming Potential (GWP) analysis for life-cycle-stages A1-A3, based on available Environmental Product Declarations (EPDs). Fibre-based reinforcements showed significant reductions in carbon footprint when considering only the reinforcement material. However, for a fair comparison, both concrete and reinforcement must be considered. Since fibre-reinforced concrete typically requires a higher cement content per 𝑚3 of concrete than steel-reinforced concrete.
GWP values per square meter of TCC floor (reinforcement only):
• Steel mesh: 4.05 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2
• Basalt fibre: 0.45 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2
GWP values for combined concrete and reinforcement:
• Steel mesh: 16.93 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2
• Basalt fibre: 17.40 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2
Comparison of results for the GWP of only reinforcement and combination of reinforcement and concrete matrix emphasizes the importance of evaluating the entire concrete-reinforcement system. To refocus on the reinforcement material, a concrete mix using eco2cem, a lower GWP cement alternative, was studied. The adjusted GWP values are:
• Steel mesh with eco2cem: 11.26 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2
• Basalt fibre with eco2cem: 11.43 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2

The analysis revealed that fibre reinforcement, when applied with the same cross-sectional height as steel mesh, results in higher GWP values. However, using low-GWP concrete and considering potential design optimizations, such as reduced cross-sectional height due to the elimination of corrosion-sensitive steel and the associated need for concrete cover, could make basalt fibre a more attractive alternative.
An additional finding was the high GWP contribution of dowels, measured at 12.97 𝑘 𝑔 𝐶𝑂2 𝑒𝑞/𝑚2 . The high GWP value for the dowels is most likely due to the high-level of detail and intervention during the manufacturing, leading to a more energy intensive process.

The findings indicate that these two performance aspects are strongly interconnected, primarily through the concrete mixture rather than the reinforcement alone. Basalt fibre reinforcement relies on its bond with concrete for structural efficiency, while the environmental impact in terms of GWP is largely determined by cement content. Using conventional fibre quantities from literature led to an overdesigned structure with a GWP exceeding that of the reference DPG TCC floor. This demonstrates that optimizing the concrete mixture is essential for achieving both structural adequacy and sustainability, even when
reinforcement selection is the primary focus.

This research demonstrates that basalt fibres can meet structural performance requirements and improve the sustainability of TCC floor systems, particularly when focusing on the reinforcement material. It also underscores the necessity of evaluating all components of the system together. The developed MCA offers a framework for assessing novel reinforcement strategies in terms of both mechanical behaviour and environmental impact.

Recommendations for future research include:
• Expanding data on bio-based fibre-reinforced concrete.
• Experimental validation of fibre-reinforced concrete behaviour.
• Development of design codes for fibre reinforcement
• More comprehensive EPDs to support life cycle assessments of emerging materials
... Read more

Study relating Acoustic Emission (AE) energy to fracture energy has been conducted in the past and a correlation has been reported between the two. The scope of these studies has remained limited to laboratory size specimens with known crack location and the energy release being investigated on a global scale. The objective of this research is to track the local energy release due to cracking in concrete using AE monitoring and understand the relationship between AE energy and crack energy estimated using nonlinear FE model. This will allow to keep the track of energy release due to cracking and use AE energy as a measure for the structural health condition. The study involves challenges with respect to AE source identification, estimating AE energy at source location accounting for attenuation losses and estimating local energy in the numerical model. These issues are discussed in detail in this thesis and the use of AE in crack monitoring is critically examined. In the first part of the thesis, AE source classification methods including signal-based approach and parameter-based approach are reviewed. The classification methods help distinguish the AE activities due to crack opening from ones related to friction. An approach for signal-based AE classification using the AE signal in the frequency domain is proposed. This approach is then compared to existing bivariate and multivariate parameter-based classification methods. In addition to this, a novel partial power-based method for AE source classification is also proposed. The existing parameter-based classification methods are found to have a similarity of less than 50% in case of bivariate methods and a little over 50 % in the case of the multivariate method when compared to the signal-based method. This is because these methods are unable to notice small differences in AE signals. On the other hand, the partial power-based method has a similarity of about 75 % to the signal-based method. In addition to this, the partial power-based method is much faster than the signal-based approach, thus providing a good alternative to the existing AE classification methods. In the second part, attenuation in AE signals is studied. Experiments on sound concrete and cracked concrete have been performed to study the attenuation in concrete media and through a crack, respectively. AE attenuation due to elastic wave propagation is made under the assumption of a Rayleigh wave and the material attenuation factor (α) is estimated to be 2.473 m-1. Crack attenuation factor (C.A.F.) is introduced to determine the energy loss through a crack. Auto Sensor Test (AST) measurements made during the experiment were used to estimate C.A.F. AST measurements are found to be sensitive to the strain changes within the concrete and are thus able to predict the occurrence of the crack in advance. In the last part, a methodology to estimate the local energy release in the numerical model is proposed and then verified using a notched beam as a test model. A rotating crack approach for modelling is adopted with tension behaviour defined using the Hordijk curve. The proposed methodology is applied to the girder model to estimate the energy released locally. The numerical energy trend thus calculated is compared to the AE energy trend at the crack location. The AE energy predicts the occurrence of the first flexure crack at 90% of the cracking load as per numerical energy. A possible explanation for this is that AE can also detect the presence of the microcracks, which the current numerical model cannot. On comparing the estimated energies released due to AE and numerical model in the flexure zone it can be concluded that the relationship between the AE energy and numerical energy is non-linear. Local energy release trend for AE and the numerical model with increasing load is similar when the flexure cracks are generated, although slight deviations start to occur when the shear crack is created. ... Read more