Accelerated and natural carbonation of concrete with high volumes of fly ash : chemical, mineralogical and microstructural effects

Today, a rather poor carbonation resistance is being reported for high-volume fly ash (HVFA) binder systems. This conclusion is usually drawn from accelerated carbonation experiments conducted at CO2 levels that highly exceed the natural atmospheric CO2 concentration of 0.03-0.04%. However, such accelerated test conditions may change the chemistry of the carbonation reaction (and the resulting amount of CH and C-S-H carbonation), the nature of the mineralogical phases formed (stable calcite versus metastable vaterite, aragonite) and the resulting porosity and pore size distribution of the microstructure after carbonation. In this paper, these phenomena were studied on HVFA and fly ash thorn silica fume (FA + SF) pastes after exposure to 0.03-0.04%, 1% and 10% CO2 using thermogravimetric analysis, quantitative X-ray diffraction and mercury intrusion porosimetry. It was found that none of these techniques unambiguously revealed the reason for significantly underestimating carbonation rates at 1% CO2 from colorimetric carbonation test results obtained after exposure to 10% CO2 that were implemented in a conversion formula that solely accounts for the differences in CO2 concentration. Possibly, excess water production due to carbonation at too high CO2 levels with a pore blocking effect and a diminished solubility for CO2 plays an important role in this

Setting control of completely recyclable concrete with slag and aluminate cements

A completely recyclable concrete (CRC) is designed to have a chemical composition equivalent to the one of general raw materials for cement production. By doing so, this CRC can be used at the end of its service life in cement manufacturing without the need for ingredient adjustments. In one of the designed CRC compositions, blast-furnace slag cement (BFSC) was combined with calcium aluminate cement (CAC), which resulted in fast setting. In an attempt to control this fast setting, different retarders and/or the combination of lime and calcium sulfate were added to the system. The workability (slump and flow), setting time (ultrasonic transmission measurements and Vicat), strength development (compressive strength tests), and hydration behavior (isothermal calorimetry) were studied. It was found that the combined addition of lime and calcium sulfate results in a workable mixture that becomes even more workable if a retarder is also added to the system

Completely recyclable concrete for a more environment-friendly construction

Although concrete is a durable material, it has a big impact on the environment due to its high production volumes. This impact is mostly related to the consumption of virgin raw materials, the production of waste and the emission of carbon dioxide. The aim of this study was to move towards a high value recycling of construction and demolition waste. Inspired by the cradle-to-cradle concept, Completely Recyclable Concrete (CRC) is designed as a raw material for clinker production, without the need for ingredient adjustments. Several CRC compositions were designed after carefully selecting suitable raw materials (e.g. fly ash, porphyry aggregates, copper slag and calcium aluminate cement). The quality and durability of these CRC mixtures was assessed with special attention to the possible applications of copper slag and the deceleration of the fast setting that resulted from the combination of calcium aluminate cement and blast furnace slag cement. The CRC clinker and cement quality were studied in depth by in situ and ex situ XRD/Rietveld analysis, light microscopy and thermal analysis. Also the applicability of an existing OPC hydration model was verified. Finally, the sustainability of the CRC concept was verified using Life Cycle Assessment

Life cycle assessment of completely recyclable concrete

Since the construction sector uses 50% of the Earth. s raw materials and produces 50% of its waste, the development of more durable and sustainable building materials is crucial. Today, Construction and Demolition Waste (CDW) is mainly used in low level applications, namely as unbound material for foundations, e.g., in road construction. Mineral demolition waste can be recycled as crushed aggregates for concrete, but these reduce the compressive strength and affect the workability due to higher values of water absorption. To advance the use of concrete rubble, Completely Recyclable Concrete (CRC) is designed for reincarnation within the cement production, following the Cradle-to-Cradle (C2C) principle. By the design, CRC becomes a resource for cement production because the chemical composition of CRC will be similar to that of cement raw materials. If CRC is used on a regular basis, a closed concrete-cement-concrete material cycle will arise, which is completely different from the current life cycle of traditional concrete. Within the research towards this CRC it is important to quantify the benefit for the environment and Life Cycle Assessment (LCA) needs to be performed, of which the results are presented in a this paper. It was observed that CRC could significantly reduce the global warming potential of concrete

Utilization of copper slag as a cementitious material in reactive powder concrete

This research studies the use of copper slag from a plant in Belgium as a cementitious material in reactive powder concrete (RPC). The quickly cooled granulated copper slag (QCS) was ground intensively using a planetary ball mill. A lower water-to-binder ratio of 0.18 was chosen for the RPC in this study. Various concrete and cement paste samples were produced with increasing copper slag contents from 0 to 20 wt% in steps of 5 wt%. Particle size distribution (PSD) and specific surface area (SSA) of the copper slag were assessed using laser diffraction and the Blaine permeability test, respectively. The results obtained, showed that the strength of RPC with different copper slag proportions was similar to or better than the control mixture at 90 days. The presence of copper slag in the paste tends to decrease the total heat production of the paste. The pozzolanic reactivity of QCS determined by the Chapelle test was found to be low

The assessment of clinker and cement regenerated from completely recyclable concrete

As the construction sector uses 50% of the earth’s raw material and produces 50% of its waste, the development of more durable and sustainable building products is crucial. Nowadays, Construction and Demolition Waste (CDW) is already used as recycled aggregates in low-value concrete applications, since it is mostly inert material. On the other hand, the general trend today for the cement industries is the use of alternative raw materials for the production of cement clinker. From this and the above mentioned need for high-value recycling of CDW, the concept of completely recyclable concrete (CRC) has been developed. After demolition of a CRC-construction, the material cycle is closed as the concrete rubble is given a second life as raw material for cement production, without need for adjustments. Therefore, the concrete mixture is designed to be chemically equivalent to raw material for cement production by adequately incorporating limestone aggregates, different types of cement and industrial by-products. For this study, completely recyclable concrete was designed and produced. Within the design process, the chemical composition of the produced CRC was evaluated with the lime saturation factor, the silica modulus, the alumina modulus and the hydraulic modulus. In addition, the potential mineralogical composition was calculated according to the formulas of Bogue. Then, clinker was regenerated by burning ground CRC in a laboratory furnace by raising the temperature at a constant rate (15 °C/min) to 1350, 1400 and 1450 °C and maintaining it for 30 minutes. After burning, the clinker was immediately air-cooled by removing it from the furnace. The quality of the produced clinker and the influence of the burning temperature thereupon were investigated by determining the free lime content, and by microscopic and X-ray diffraction analysis. Based on these results, the ideal burning temperature was selected to produce cement. This cement was produced by grinding the clinker with calcium sulphate anhydrite. The hydration heat of cement pastes was measured in isothermal conditions and mortars were produced for compressive strength test

Results of a worldwide survey on the currently used histopathological diagnostic criteria for invasive lobular breast cancer

Invasive lobular carcinoma (ILC) represents the second most common subtype of breast cancer (BC), accounting for up to 15% of all invasive BC. Loss of cell adhesion due to functional inactivation of E-cadherin is the hallmark of ILC. Although the current world health organization (WHO) classification for diagnosing ILC requires the recognition of the dispersed or linear non-cohesive growth pattern, it is not mandatory to demonstrate E-cadherin loss by immunohistochemistry (IHC). Recent results of central pathology review of two large randomized clinical trials have demonstrated relative overdiagnosis of ILC, as only similar to 60% of the locally diagnosed ILCs were confirmed by central pathology. To understand the possible underlying reasons of this discrepancy, we undertook a worldwide survey on the current practice of diagnosing BC as ILC. A survey was drafted by a panel of pathologists and researchers from the European lobular breast cancer consortium (ELBCC) using the online tool SurveyMonkey (R). Various parameters such as indications for IHC staining, IHC clones, and IHC staining procedures were questioned. Finally, systematic reporting of non-classical ILC variants were also interrogated. This survey was sent out to pathologists worldwide and circulated from December 14, 2020 until July, 1 2021. The results demonstrate that approximately half of the institutions use E-cadherin expression loss by IHC as an ancillary test to diagnose ILC and that there is a great variability in immunostaining protocols. This might cause different staining results and discordant interpretations. As ILC-specific therapeutic and diagnostic avenues are currently explored in the context of clinical trials, it is of importance to improve standardization of histopathologic diagnosis of ILC diagnosis