8th International Symposium on Sustainable Biochar, Cement and Concrete Production and Utilization

In recent years, biochar has been successfully investigated to improve the mechanical properties, internal curing, and CO₂ capture of cementitious materials [1]. Thus, the aim of this work was to study the sensing ability of commercial biochar (Nera biochar) made from certified wood wastes as a strain sensor in mortar samples.

The as-received material was first characterized by laser granulometry, X-ray diffraction, x-ray fluorescence and scanning electron microscopy. Later, the biochar particles were manually ground and sieved at 125 microns with a steel mesh. The passing fraction was first dispersed in distilled water using a bath sonicator and then, added to a commercial resin for restoration (Primal B60 from Rohm & Haas, a copolymer of ethyl acrylate/methyl methacrylate) under magnetic stirring. Multiwalled carbon nanotubes (CNTs, Nanocyl 7000) were also used to increase the sensitivity of the sensors because of their higher aspect ratio. Different compositions were investigated: pure biochar, 85% biochar/15% CaCO₃, 80% biochar/20% CaCO₃, 65% biochar/15% CaCO₃/20% CNTs and 60% biochar/20% CaCO₃/20% CNTs. Two stainless steel mesh (1 × 2 cm²) were manually inserted as electrodes into mortar prisms (4 × 4 × 16 cm³) prepared with standard sand immediately after casting and vibrating (1:2 water to cement ratio and 3:1 sand to cement ratio). The samples were demolded after 24 hours and cured under water for 28 days. After drying, the sensing materials were finally painted by brush on the cementitious samples (strip of 1 cm in width between the two stainless steel electrodes at a distance of about 10 cm). 

The prisms were tested in three-point bending, and the sensing films were alimented with a 1 V AC current at 1 kHz frequency using an impedancemeter (Hioki 3301). The change in the impedance value was monitored during mechanical testing. The measurements were first done on samples with a certain humidity content and then on fully dried ones. The best results were obtained with the sensing film containing 60% biochar/20% CaCO₃/20% CNTs, which showed a 23% change in the impedance value under a force of 2000 N.

Biochar is a carbonaceous material derived from the pyrolysis of biomass, which is often considered a waste material with the associated disposal problems. In this work will be summarises the latest research developments in biochar materials, a field that is gaining increasing popularity due to biochar's potential to replace carbon materials derived from non-renewable sources. The work explores emerging and innovative applications of biochar, covering all aspects of the field, from production [1] to applications, including details on the techniques used. Special attention is given to biochar as a material for composites and sensors [2]. 

The applications of biochar in the field of cement-based composites will also be discussed as it is expected that the cement industry will have a high demand for biochar in the coming years as biochar has proven to be an excellent substitute for both inert material and cement itself without altering the properties of the final composite.

This work has been reported in the first book [3] to address the emerging applications of biochar as an innovative, versatile and renewable carbon-based material, going beyond its traditional uses in agriculture. The book is a valuable reference for all researchers in the field of biochar and carbon-based materials, including practitioners.

The concrete industry is one of the major consumers of natural resources. Sustainable development aims to find alternative resources that could decrease the concrete industry's adverse effects on the environment and contribute to preserving natural resources. Vast amounts of waste tires accumulated worldwide are recognized as a good supplement for natural aggregates in concrete [1]. Shredded rubber is generally used as a substitute for coarse aggregate, irregularly shaped crumb rubber is used as a fine aggregate, and powdered rubber can be used as a filler, binder, or fine sand in concrete [2]. Concrete with recycled rubber has many advantages over standard concrete, such as more excellent ductility, lower thermal conductivity, and better resistance to freezing and thawing [3]. However, mechanical strength is generally reduced when the natural aggregates in standard concrete are replaced by rubber.

This study aimed to design load-bearing concrete in which fine aggregate was partially replaced by crumb rubber in the 5-20 % range by volume. Workability, compressive strength, density, dynamic modulus of elasticity, freeze-thaw resistance, and induced volume changes were comprehensively evaluated. The consistency of the rubberized concrete and the strength loss in the hardened state was compensated by adding a superplasticizer and silica fume. The results show that the modified concrete maintains its compressive strength and provides better freeze-thaw protection than standard concrete.

Research in biochar concrete has advanced considerably in the last 11 years or so.  However, there is not yet any study examining the effects of biochar on the mechanical strength, net embodied carbon and effectiveness of accelerated carbonation of a relatively new and more sustainable type of concrete - limestone calcined clay concrete (LC3). 

This work represents a pioneering effort in examining the influence that rice husk- and wood-based biochar, produced at a temperature range of 300-500C, have on the aforementioned qualities of LC3-70, in which 30% of the Ordinary Portland Cement (OPC) was replaced with the combination of limestone, calcined clay and sustainable additives. Four types of additives were examined: rice husk ash (RHA), rice husk biochar, wood sawdust protected with titanium dioxide shell, and sawdust biochar. These samples were further categorized into two groups - those dosed with CO2 (i.e. accelerated carbonation at 20% over 24 hours) and those that were not dosed. 

It was observed that accelerated carbonation marginally increased the compressive strength (by 2-5%) of all samples containing the aforementioned sustainable additives at 28 days. However, all these samples had marginally lower strength than the control LC3-70, except when RHA was used (a 1.6% increased strength was observed). Furthermore, the compressive strength of the samples was not correlated to the quantities of calcium hydroxide produced from hydration of the binder. 

The most notable result in this study was that carbonation of these LC3 samples made them more resilient to heat - thermogravimetric analyses reviewed that carbonation substantially reduced the disintegration of the calcium carbonate (calcite) present in all the LC3-70 samples. This unusual phenomenon can be attributed to the production of additional amounts of alumina and silica gels in the matrix, which increased the internal thermal resistance of the microstructure of the LC3-70. 

These results show that substituting OPC in LC3-70 with the proposed sustainable additives does not affect the strength significantly, but it can reduce the net carbon emission of the concrete while rendering the mix more resistant against thermal disintegration. This special characteristic implies that our mixes can potentially be used as indoor lightweight non-structural panels that can be used to prevent fire from spreading within a particular confined indoor space.

This case study provides a holistic perspective on the emerging biochar production industry in Mexico, focusing on the industry as a whole rather than individual companies. The study explores the industry's initiatives to harness agricultural waste for sustainable biochar product creation, with shared objectives of boosting local economic development, addressing climate change, and capitalizing on carbon markets.

Leveraging successful experiences in various emerging markets [2], the industry recognized the promise of biochar in supply chain innovation and systems optimization. Mexico, endowed with an ample supply of agricultural waste, emerged as a promising market. However, the challenge remained in familiarizing the market with biochar, an unfamiliar product in this context.

The industry embraced a proactive approach by collaborating with farming organizations and local communities, aiming to garner support and introduce biochar to the Mexican market through consistent communication, education, and practical demonstrations.

The study addresses the economic viability of biochar production in Mexico, driven by secure feedstock sources and anticipated revenue from carbon credits. The timeline for biochar production, its primary application in traditional agriculture, and ongoing experiments for efficiency optimization are presented as common industry practices.

Biochar producers in Mexico are exploring non-agricultural markets [1], such as the construction sector, where biochar can enhance construction materials and reduce carbon emissions. Collaborations with industry associations and research institutions support these initiatives.

The study discusses the projection of carbon credit revenue growth, on the expanding voluntary market and the increasing confidence in testing and data disclosure, which can boost biochar's financial sustainability.

The report concludes with a set of recommendations for aspiring biochar producers, emphasizing the importance of securing feedstock, assessing local market potential, and conducting studies to foster industry growth..