Stress-Crack Separation Relationship for Macrosynthetic, Steel and Hybrid Fiber Reinforced Concrete

An experimental evaluation of the crack propaga tion and post-cracking response of macro fiber reinforced concrete in flexure is c onducted. Two types of structur al fibers, hooked end steel fibers and continuousl y embossed macro-synthetic fibers are used in this study. A fiber blend of the two fibers is evaluated for spec ific improvements in the post peak residual load carrying response. At 0.5% volume fraction, both steel and macrosynthetic fiber reinforced concrete exhibits load recovery at large crack opening. The blend of 0.2% macrosynthetic fibers and 0.3% steel fibers shows a significa nt improvement in the immediate post peak load response with a significantly smaller load drop and a constant residual load carrying capacity equal to 80% of the peak load. An analytical formulation to predict fle xure load-displacement behaviour considering a multi-linear stress- crack separation (σ -w) relationship is developed. An inverse analysis is developed for obtaining the multi- linear σ -w relation, from the experimental response. The � -w curves of the steel and macrosynthetic fiber reinforced concrete exhibit a stress recovery after a significant drop with increa sing crack opening. Significant residual load carrying capacity is attained only at large crack separation. The fiber blend exhibits a constant residual stress with increasing crack sepa ration following an initial decrease. The constant residual stress is attained at a small crack separation

Advances in Binders for Construction Materials

The global binder production for construction materials is approximately 7.5 billion tons per year, contributing ~6% to the global anthropogenic atmospheric CO2 emissions. Reducing this carbon footprint is a key aim of the construction industry, and current research focuses on developing new innovative ways to attain more sustainable binders and concrete/mortars as a real alternative to the current global demand for Portland cement.With this aim, several potential alternative binders are currently being investigated by scientists worldwide, based on calcium aluminate cement, calcium sulfoaluminate cement, alkali-activated binders, calcined clay limestone cements, nanomaterials, or supersulfated cements. This Special Issue presents contributions that address research and practical advances in i) alternative binder manufacturing processes; ii) chemical, microstructural, and structural characterization of unhydrated binders and of hydrated systems; iii) the properties and modelling of concrete and mortars; iv) applications and durability of concrete and mortars; and v) the conservation and repair of historic concrete/mortar structures using alternative binders.We believe this Special Issue will be of high interest in the binder industry and construction community, based upon the novelty and quality of the results and the real potential application of the findings to the practice and industry

SynerCrete’18: interdisciplinary approaches for cement-based materials and structural concrete: synergizing expertise and bridging scales of space and time, vol. 2

info:eu-repo/semantics/publishedVersio

Natural hydraulic lime mortars for use in high temperature, high humidity climatic conditions : effect of calcitic fillers

The widespread adoption of alternative binders are playing an increasing role in carbon dioxide (CO2) abatement in green construction and the repair of traditionally built structures. Natural Hydraulic Lime (NHL) has better environmental credentials than Portland Cement (PC) due in part to its lower calcination temperature and its ability to absorb CO2 during carbonation. However, NHL is more sensitive to climatic conditions during the setting and hardening processes and this is especially pronounced in high humidity climates. This research investigated the influence of various types of calcitic fillers (oyster shells, limestone, marble and precipitated calcium carbonate (PCC)) modifications to NHL mortars subjected to high temperature and humidity environments and evaluated the subsequent effect on early development of various chemical and physical properties. Primary mortar parameters such as moisture loss, pH, carbonation depth, flexural strength, compressive strength, sorptivity and microscopy analysis (SEM images) were studied. The results showed that the setting and hardening of those mortars with precipitated calcium carbonate worked most effectively in high humidity environments. The purity and crystallinity of the mineral ‘seeding’ materials was attributed to the positive benefits in the physical characteristics. Additionally, curing at higher temperatures greatly accelerated the hydration reaction of the mortar. It is evident from the findings that modified mortars can increase the performance especially in terms of carbonation rate, flexural strength, compressive strength and sorptivity. Whilst the precipitated calcium carbonate showed positive benefits in early stage setting reactions it did not significantly influence the long term physical characteristics of the mortars. This situation is meaningful for our understanding of modified lime mortars and the seeding materials. This research can be used to influence the specification and product design of NHL materials in high temperature and high humidity environments and this is especially important for its early stage use that has been traditionally associated with reduced set characteristics

Sustainable Geotechnics—Theory, Practice, and Applications

Today, modern Geotechnical Engineers, who in the past would have considered the phenomena occurring in the (primarily soil) environment, are faced with developments in environmental sciences that are becoming increasingly more detailed and sophisticated, with the natural phenomena and processes surrounding the civil engineering infrastructure being modeled, designed, monitored, and assessed in a more holistic way. This book brings together the state of the art in geotechnics with a focus on sustainable design, resilience, construction, and monitoring of the performance of geotechnical assets from ground investigations, through foundation and drainage design to soil stabilization and reinforcement. Engineers and scientists working in the fields of green infrastructure, nature-based solutions, sustainable drainage, eco-engineering, hydro-geology, landscape planning, plant science, environmental biology or bio-chemistry, earth sciences, GIS, and remote sensing are represented here by articles that show significant geotechnical components or applications. Case studies showcasing the application of the sustainable development principles (e.g., reuse, recycle, reduce; stakeholder engagement; public health; UN Global Sustainability Goals) in Geotechnics are also included in this book

Effects of Nanoparticles (Al2O3 and TiO2), Fibers and Fly Ash on Cementitious and Non-cementitious Materials at Room Temperature and 80°C Curing Temperature: Experimental and Empirical Modelling Studies

Cement constitutes undoubtedly one of the most important well barrier elements, in terms of maintaining well integrity by preventing undesired flow of reservoir fluid into the wellbore. NORSOK D-010 standard dictates that well cement must be impermeable, non-shrinking, ductile and resistant to corrosion among other requirements to ensure long term integrity of the wells [1]. Although, various surveys have found that conventional well cement have serious shortcomings that are the reasons for compromising well integrity globally. It was discovered in 2003 that 8000 to 11000 wells in GOM experienced SCP due to compromised cement integrity as the ages of the wells increased [2]. In 2008, cement failure induced well integrity issues were detected in around 10.7% of 75 NCS wells from a total of 406 well that were included in this study [3]–[4]. Poor cement qualities affect the environment as well. Reported in 2013, authorities in Pennsylvania had issued notices of environmental violations to 1144 wells out of 3533 wells, where 8.7% violations originated from poor cement and casing quality that led to environmental pollution [5]. These investigations reveal that cement in its neat form fails to maintain permanent zonal isolation in wells. It goes without saying, the current cement properties do not meet the regulatory requirements. This is why investigations were conducted to improve the mechanical and rheological properties. Applications of nanotechnology have spread over numerous industries. Numbers of research publications concerning the implementations of nanotechnology are ever growing with time and some studies have shown to have obtained promising results using different metallic nanoparticles. Consequently, Al2O3 and TiO2 nanoparticles (NPs) were considered to be investigated in conjunction with G-class Ordinary Portland Cement (OPC), fly ash (FA), geopolymer cement, carbon fibers (CF) and white glass fibers (WF). Moreover, two different curing environments of room temperature of 20°C and oven temperature of 80°C were introduced to study the temperature effects on the nano-modified cementitious and non-cementitious materials. Because the conventional cement gets degraded when exposed to high temperature for a long time. In terms of experimental structures, total of five test designs were constructed. Four test designs were made with OPC had curing ages of 3, 7 and 28 days and they were cured in both room and oven. One design consisting of geopolymer cement were mainly cured in room temperature for a period of 10 days. Lower concentration of Al2O3 NPs seemed to improve the uniaxial compressive strength (UCS) of OPC by 100.1% in room and 24.8% in oven after 28 days of curing. OPC modified with solitary FA and binary hybrid of FA and intermediate Al2O3 had shown improvement in early strength after 3 and 7 days. However, after 28 days, solitary and binary blend of FA showed opposing results. Medium concentration of TiO2 NPs significantly improved the UCS of geopolymer cement by 41.8%. When applied in OPC, lowest dosage of TiO2 improved the strength of OPC plug by 19.2% in room temperature after 28 days, whereas the highest concentration performed the best in oven with 42.1% UCS raise. With an intention to potentially reducing cement’s brittleness, CF and WF were added with TiO2 as respective binary hybrids to OPC, which had presented with very optimistic results. Generally, TiO2 with highest dosage of CF had shown the most improvements in OPC strength developments in both curing environments. The stiffness, energy absorption capacity and modulus of elasticity of the samples were also analysed, however there were no clear trends of the developments of these properties. Rheological properties for the additives-modified OPC slurries were determined to have workability and slurries were comparatively pumpable, whilst nano-added geopolymer cement was highly viscous for the given LSR. The internal structures of nano-added OPC and geopolymer plugs were analysed with SEM. An empirical UCS vs compressional wave velocity (vp) model was developed from the experimental data from this thesis and it was subsequently tested with three other models to verify its competence and was found to be quite fitting