Explore the vast range of titles available.

Lightweight concrete has a history of more than two-thousand years and its technical development is still proceeding. This review starts with a retrospective that gives an idea of the wide range of applications covered by lightweight concrete during the last century. Although lightweight concrete is well known and has proven its technical potential in a wide range of applications over the past decades, there are still hesitations and uncertainties in practice. For that reason, lightweight aggregate properties and the various types of lightweight concrete are discussed in detail with a special focus on current standards. The review is based on a background of 25 years of practical and theoretical experience in this field. One of the main challenges in designing lightweight concrete is to adapt most of design, production and execution rules since they often deviate from normal weight concrete. Therefore, aspects are highlighted that often are the cause of misunderstandings, such as nomenclature or the informational value of certain tests. Frequently occurring problems regarding the mix design and production of lightweight concrete are addressed and the unintended consequences are described. A critical view is provided on some information given in existing European concrete standards regarding the mechanical properties of structural lightweight concrete. Finally, the latest stage of development of very light lightweight concretes is presented. Infra-lightweight concrete is introduced as an innovative approach for further extending the range of applications of lightweight concrete by providing background knowledge and experiences from case records.

This study investigated the effects of NaOH molarity (6–14 M) and ground granulated blast furnace slag (GBFS) content (0–45%) on the properties of lithium slag (LS)-based cold-bonded lightweight aggregates. Bulk density, water absorption, porosity, and cylinder compressive strength were evaluated, and microstructural characterization was conducted using SEM, XRD, FTIR, MIP, and TG/DTG. Results showed that increasing NaOH molarity and GBFS content reduced water absorption (from 15.87 to 5.88%) and porosity (from 34.79 to 13.39%), while enhancing bulk density (731–1074 kg/m³) and compressive strength. At 30% GBFS, the 28-day strength increased by 224.48%, from 3.35 MPa (M6-30) to 10.87 MPa (M14-30). At 12 M NaOH, raising GBFS content from 0 to 45% increased strength by 435.62%, from 2.33 MPa to 12.48 MPa. LS without GBFS achieved 2.33 MPa, indicating inherent pozzolanic activity. Microstructural analysis revealed that performance improvement was due to enhanced geopolymerization and reduced harmful pores (> 200 nm). The M8-30 mix (915.68 kg/m³, 5.98 MPa) showed potential for meeting high-strength lightweight aggregate criteria with mix optimization. These findings demonstrate the feasibility of valorizing LS into high-performance lightweight aggregates, contributing to waste utilization and low-carbon construction.

Lightweight aggregates are a material used in many industries. A huge amount of this material is used in construction and architecture. For the most part, lightweight construction aggregates are obtained from natural resources such as clay raw materials that have the ability to swell at high temperatures. Resources of these clays are limited and not available everywhere. Therefore, opportunities are being sought to produce lightweight artificial aggregates that have interesting performance characteristics due to their properties. For example, special preparation techniques can reduce or increase the water absorption of such an aggregate depending on the needs and application. The production of artificial lightweight aggregate using various types of waste materials is environmentally friendly as it reduces the depletion of natural resources. Therefore, this article proposes a method of obtaining artificial lightweight aggregate consolidated using two methods: drum and dynamic granulation. Hardening was achieved using combined methods: sintering and hydration, trying to maintain the highest possible porosity. Waste materials were used, such as dust from construction rubble and residues from the processing of PET bottles, as well as clay from the Bełchatów mine as a raw material accompanying the lignite overburden. High open porosity of the aggregates was achieved, above 30%, low apparent density of 1.23 g/cm 3 , low leachability of approximately 250 µS. The produced lightweight aggregates could ultimately be used in green roofs.

Global concrete production, reaching 14×1013m3/year, raises environmental concerns due to the resource-intensive nature of ordinary Portland cement (OPC) manufacturing. Simultaneously, 32.7×109 kg/year of expanded polystyrene (EPS) waste poses ecological threats. This research explores the mechanical behavior of lightweight concrete (LWAC) using recycled EPS manufactured with a hybrid cement mixture (OPC and alkali-activated cement). These types of cement have been shown to improve the compressive strength of concrete, while recycled EPS significantly decreases concrete density. However, the impact of these two materials on the LWAC mechanical behavior is unclear. LWAC comprises 35% lightweight aggregates (LWA)—a combination of EPS and expanded clays (EC) — and 65% normal-weight aggregates. As a cementitious matrix, this LWAC employs 30% OPC and 70% alkaline-activated cement (AAC) based on fly ash (FA) and lime. Compressive strength tests after 28 curing days show a remarkable 48.8% improvement, surpassing the ACI 213R-03 standard requirement, which would allow this sustainable hybrid lightweight aggregate concrete to be used as structural lightweight concrete. Also obtained was a 21.5% reduction in density; this implies potential cost savings through downsizing structural elements and enhancing thermal and acoustic insulation. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal the presence of C-S-H, C-(A)-S-H, and N-A-S-H gels. However, anhydrous products in the hybrid LWAC suggest a slower reaction rate. Further investigation into activator solution dosage and curing temperature is recommended for improved mechanical performance on the 28th day of curing. This research highlights the potential for sustainable construction incorporating waste and underscores the importance of refining activation parameters for optimal performance.

Infrastructure development and urbanization have created a demand for the prime construction material—\"Concrete.\" The manufacture of concrete has pressurized the aggregate supply chain for over-exploitation of natural resources leading to eco-detrimental impacts besides environmental regulations. The auxiliary sectors of the construction industry are creating a vast quantum of by-products and waste, causing environmental degradation, which concerns governing bodies. Developing aggregates artificially using these by-products and waste materials would be an eco-friendly and economical solution. This article provides an overview of the ingredients, production methods, and factors influencing the characteristics of such sustainable building materials, which can substitute conventional aggregates in the near future.

Low density, fire resistance and good thermal insulation properties of lightweight aggregate concrete (LWAC) have drawn the attention of engineers and researchers for its widespread application. However, the LWAC still found limited application in the construction industry. For conventional application of LWAC, knowledge of different attributes of its behaviour is needed, and thus the presented review investigates the comprehensive studies on LWACs incorporating lightweight aggregates (LWAs) i.e. oil palm shell, lightweight expanded clay aggregate (LECA), fly ash-sintered (FS) and pumice, along with supplementary cementitious materials (SCMs). Firstly, the physico-chemical, morphological and mineralogical characterization of different LWAs is presented, followed by critical review on fresh, hardened, durability and thermal properties of LWACs vis-a-vis normal weight concrete. Furthermore, research works conducted on the development of LWACs using LECA, fly ash and micro-fine slurry powder (MSP) are discussed. Research findings show that LWAC prepared with LECA as coarse and fine aggregate along with 25% fly ash + 10% MSP as cement replacement exhibits good mechanical and thermal properties. Overall, it has been envisaged that LWACs, because of their techno-economic and environmental advantages, are supposed to capture a major share in the building industry in the twenty first century. Basically, the scientific contribution of the present work is to provide the knowledge base and scientific basis for further research in this area and lay the foundation for the development of the guidelines to use LWACs. Graphical abstract

The present study aims to characterize the capillary absorption of structural lightweight aggregate concrete (LWAC), taking into account different compositions with lightweight aggregates (LWA) of very distinct porosity. The influence of the following parameters is analysed: the volume and initial water content of LWA; the cement content and its replacement by fly ash or silica fume; the partial replacement of normal weight aggregate by lightweight coarse or fine aggregate; different curing conditions. It is shown that LWAC usually has higher initial and long-term absorption than normal weight concrete (NWC) of the same composition. However, the sorptivity tends to be similar in both concretes, regardless of the type and volume of aggregate and the water/cement of the surrounding paste. Moreover, the sorptivity is lower in LWAC than in NWC of the same strength. It is also shown that the coarser the porosity of the LWA the lower is the capillary action. The capillary absorption is higher in LWAC with pre-soaked LWA and increases as the percentage replacement of cement by fly ash increases and the percentage of silica fume decreases.

The interfacial transition zone (ITZ) significantly influences the mechanical properties and durability of lightweight aggregate concrete (LWAC), yet existing research on the ITZ in LWAC remains fragmented due to varied characterization techniques, inconsistent definitions of ITZ thickness and porosity, and the absence of standardized performance metrics. This review focuses primarily on structural LWAC produced with artificial and natural lightweight aggregates, with intended applications in high-performance civil engineering structures. This review systematically analyzes the microstructure, composition, and physical properties of the ITZ, including porosity, microhardness, and hydration product distribution. Quantitative data from recent studies are highlighted—for instance, incorporating 3% nano-silica increased ITZ bond strength by 134.12% at 3 days and 108.54% at 28 days, while using 10% metakaolin enhanced 28-day compressive strength by 24.6% and reduced chloride diffusion by 81.9%. The review categorizes current ITZ enhancement strategies such as mineral admixtures, nanomaterials, surface coatings, and aggregate pretreatment methods, evaluating their mechanisms, effectiveness, and limitations. By identifying key trends and research gaps—particularly the lack of predictive models and standardized characterization methods—this review aims to synthesize key findings and identify knowledge gaps to support future material design in LWAC.

An experimental program was conducted to investigate the mechanical, fracture, and physical properties of self-consolidating lightweight concretes (SCLCs) made with cold-bonded fly ash (FA) aggregates. A total of 17 SCLCs were designed with a water-binder ratio (w/b) of 0.32, in which the natural aggregates were partially replaced with cold-bonded lightweight fine aggregate (LWFA) and lightweight coarse aggregate (LWCA) at different volume fractions of 10, 20, 30, 40, and 50%. Hardened properties of the SCLCs were tested for bond strength, fracture energy, characteristic length, drying shrinkage, weight loss, and restrained shrinkage cracking. It was observed that the SCLCs had relatively lower compressive and splitting tensile strengths with increasing LWFA and/or LWCA in the mixtures. Bond strength of the SCLCs decreased gradually with the replacement level of LWA because the bond strength directly depended on the quality of the cement paste and aggregate. Although SCLCs had significantly poorer restrained shrinkage cracking performance than the control concrete, the time to cracking greatly lengthened as the replacement level of LWA increased. Keywords: fracture; hardened properties; lightweight aggregate; pelletization method; self-consolidating lightweight-aggregate concrete.

Taiwan has used technology in reservoir sediments and industrial waste to produce high-performance lightweight aggregate (LWA). LWA can be used to manufacture lightweight aggregate concrete (LWAC) with structural strength ratings. At present, Taiwan’s offshore wind turbines are gradually developing and are moving from coastal areas to deep-sea areas. With this in mind, this study aimed to investigate the feasibility of applying LWAC with synthetic LWA from reservoir sediments to floating offshore wind turbine foundations. LWAC and normal-weight concretes (NWC) of different strengths were prepared, and their fresh, hardened, and durability properties were tested. In addition, reinforced concrete and steel sheets were immersed in a tank of high salinity seawater to examine their resistance to seawater-accelerated corrosion. The test results showed that the total passing charge of the two groups of concrete within six hours was less than 1000 coulombs. Both groups of concrete were classified as having “Very Low” chloride permeability. The average corrosion potential of most reinforced concrete specimens was found to be greater than −200 mV, which means that the corrosion probability of the steel bars was less than 10%. Furthermore, the use of coatings for seawater corrosion protection on steel sheets was not found to be as effective as reinforced concrete. This shows that the use of LWAC with synthetic LWA from reservoir sediments for the floating foundations of offshore wind turbines is feasible and has design flexibility.