Optimization of properties of fly ash aggregates for high-strength lightweight concrete production

The optimization of properties of lightweight fly ash aggregates for suitability in high-strength lightweight fly ash concrete production was investigated using response surface methodology (RSM). Design-Expert software was used to establish the design matrix and to analyze the experimental data. The relationships between the sintering parameters (temperature, binder content and binder type) and experimentally obtained three responses (specific gravity, water absorption and crushing strength) were established. Also, the optimization capabilities in Design-Expert software were used to optimize the sintering process. Historical data design technique under RSM was performed to optimize the input parameter interactions which showed the best conditions for preparation of fly ash pellets. According to the obtained results, the developed models are statistically accurate and can be used for further analysis. The experimental values agreed with the predicted ones, thus indicating suitability of the model employed and the success of RSM in optimizing the sintering conditions.     

Ferrocement encased lightweight aerated concrete: A novel approach to produce sandwich composite

This paper presents the experimental study to investigate the applicability of a novel technique to produce lightweight sandwich composite elements. Sandwich composite is fabricated by encasing lightweight aerated concrete as core with high performance ferrocement box as skin layer. The performance of the sandwich elements is investigated in terms of ultimate compressive strength, flexural strength, water absorption, overall unit weight and the failure mode. The results are compared with control specimens made solely of the aerated concrete. Results showed the remarkable enhancement in the compressive strength and flexural strength while the water absorption is reduced to fractions as compared to that of the control specimens. Overall unit weight of the sandwich composite elements falls in the range of the lightweight structural elements. The failure mode of the sandwich elements reveals the ductile and composite behavior thus transforming a pure brittle material (aerated concrete) into ductile composite material because of the ferrocement encasement.     

Aerated lightweight concrete

RILEM Recommendations51-ALC RILEM Technical Committee

Aerated lightweight concrete     

A simple mix design method for structural lightweight aggregate concrete

Current design methods for structural lightweight aggregate concrete (SLWAC) are usually only valid for a limited range of concrete compositions that have previously been subjected to trial tests. The SLWAC mix design is more complex than that of normal weight concrete as more parameters need to be determined. Taking this into account, a simplified design method is proposed for SLWAC made with natural sand. The major advantages of the proposed method are that it is easy to apply and it can be generalized to any type of lightweight aggregate (LWA). For this, three additional design parameters are needed: the strength of LWA in concrete; the limit strength; the SLWAC potential strength. At most, two experimental mixtures are needed to determine these parameters. A biphasic model to estimate the strength of SLWAC is evaluated and high correlations are obtained. The good performance of the suggested method is demonstrated by examples of practical application and by the comparison with experimental results reported by the authors and other investigators.     

New production process for insulation blocks composed of EPS and lightweight concrete containing pumice aggregate

This study introduces a new production method for production of the insulation blocks made of pumice aggregate, lightweight concrete and expanded polystyrene foam (EPS). Products produced via this method were analyzed for compliance with the Turkish standards institution (TS EN) standards. A single-line lightweight masonry block with 200?mm?×?400?mm?×?200?mm dimension (width?×?length?×?height) was produced to produce an insulation block by using circular saw block cutting machine for the first time. Physical and thermal properties of the all-in aggregate pumice used in lightweight aggregate were determined and the all-in aggregate pumice was subjected to sieve analysis. After the production, insulation blocks were subjected to some analysis according to pre-set standards to determine their usability as masonry unit. After the curing period (28?days), it was found that the highest value of deviation from the plane was 0.150?mm; deviation of the flanges from plain parallelism was 0.40?mm; dry density was 562?kg/m³; compressive strength value was 2.99?N/mm²; water absorption coefficient by capillaries was 20.63?g/mm²sn^0.5; sound absorption value of the masonry unit was 60 (dB); thermal conductivity coefficient was 0.33?W/mK; initial shear strength value was 0.471?N/mm² and plaster-holding capacity was considerably high. When compared to other construction elements, thermal conductivity and masonry unit weight of the insulation block and masonry costs were found to be lower.     

Estimation of water absorbed by expanding clay aggregates during structural lightweight concrete production

The estimation of water absorption in aggregates is still one of the major challenges related to the production of structural lightweight aggregate concrete (SLWAC). At present these predictions are only based on common practice and a more soundly based approach is required. Aggregate absorption is mainly affected by its microstructure, surface characteristics, percentage of broken particles, initial water content and characteristics of the surrounding mortar. These are the key parameters taken into account in this paper, where the absorption of different types of Iberian aggregates with varying initial water content is analysed in detail. Based on experimental tests, and by introducing new parameters which take into account the microstructure and water content of the aggregates, a new procedure for predicting absorption by aggregates in concrete is suggested. This procedure will make it possible to more accurately specify the amount of mixing water to be used in SLWAC production, and it is almost independent of the type of aggregate. Therefore, the proposed method should be easily extended to other types of aggregate. Finally, the proposed method was checked experimentally by producing several concrete mixtures, and the results were promising.     

Mechanical properties of lightweight ceramic concrete

Concrete produced using a magnesium phosphate binder can exhibit faster strength gain and result in lower overall environmental impacts than concretes produced with Portland cement binders. This paper reports a study to develop and characterize the rheological and mechanical properties of lightweight ceramic concretes (LWCC) that use a magnesium potassium phosphate binder. The aggregate type and the overall mix composition were primary variables in the study. Aggregate types included expanded clay, expanded slate, and expanded shale. Crushed bottom ash aggregate from a local coal-fired thermal generating station was also used. The aggregates of a given material varied by size fraction and by surface characteristics in some cases. The test results showed that increases in the water/binder ratio increased the slump flow but had negligible influence on the setting time. The compressive strength and density of the LWCCs both decreased with increases in the aggregate/binder mass ratio and the water/binder ratio, regardless of the type of lightweight aggregate. The 28 day compressive strength and density ranged from 17 to 36 MPa and 1600 to 1870 kg/m³ respectively. Regardless of the aggregate type, increasing the water/binder ratio also reduced the elastic modulus, modulus of rupture and direct shear strengths. Relationships were developed to directly relate these mechanical properties to the corresponding compressive strengths. The results indicate that LWCCs using a magnesium phosphate binder and lightweight aggregates can be formulated with rheological and mechanical properties suitable for structural applications.     

The use of pumice lightweight concrete for masonry applications

In the last two decades, the use of pumice as lightweight aggregate for concrete in structural applications has been the object of different studies. The aim was to find out if pumice can be an alternative to ordinary lightweight aggregate. The present paper is framed in this context. Here, a study is presented showing the use of pumice for making lightweight concrete units for masonry members. Through the paper, the formulation of a mix design for lightweight concrete is proposed. Then the obtained mechanical characteristics of the masonry units are discussed and compared to the code requirements. Reinforced bearing masonry walls, made with the concrete masonry units in question, were made and tested under lateral cyclic loads. For comparison, lightweight concrete units and bearing walls made using expanded clay were constructed and tested in order to show if pumice can also be considered as an alternative to ordinary lightweight aggregate in the case discussed here.     

A simple novel constitutive equation for concrete

A simple novel constitutive equation, three parameter strength criterion for concrete is proposed to represent the composite nature and complex failure mechanism of material of concrete. In this paper, the study is to demonstrate the use of scalar valued function, invariant theory, as applied to concrete failure prediction. Without the loss of accuracy of prediction, a three parameter strength criterion is developed.     

A plasticity concrete material model for DYNA3D

Lagrangian finite element codes with explicit time integration are extensively used for the analysis of structures subjected to explosive loading. Within these codes, numerous material models have been implemented. However, the development of a realistic but efficient concrete material model has proven complex and challenging.

The plasticity concrete material model in the Lagrangian finite element code DYNA3D was assessed and enhanced. The main modifications include the implementation of a third, independent yield failure surface; removal of the tensile cutoff and extension of the plasticity model in tension; shift of the pressure cutoff; implementation of a three invariant formulation for the failure surfaces; determination of the triaxial extension to triaxial compression ratio as a function of pressure; shear modulus correction; and implementation of a radial path strain rate enhancement. These modifications insure that the response follows experimental observations for standard uniaxial, biaxial and triaxial tests in both tension and compression, as shown via single element analyses. The radial path strain rate enhancement insures constant enhancement for all those tests. As a full scale example, a standard dividing wall subjected to a blast load is analyzed and the effects of the modifications assessed.     

Internal curing of concrete using lightweight aggregates

Internal cured concrete (ICC) has been recently used in the local and international construction markets. ICC contains surplus amount of water to compensate the shrinkage of the mix and the volumetric changes which result in early-age cracking of concrete. Concrete cracking is a direct result of the shrinkage of the water–cement paste during early stages of the hydration process and continues for a significant amount of time during the life span of the concrete section. Early-stage shrinkage, prior to the concrete hardening, is associated with volumetric changes, until final setting is achieved. Afterward, the reduction in cement paste particle size results in increased voids within the concrete structure. These voids result in increased permeability, additional sulfate and chloride attacks on steel reinforcement, and internal tensile stresses in concrete, which result in significant cracking. ICC uses the additional water added to the mix in counteracting the reduced volume of the concrete. Several techniques are used for internal curing (IC). In this research, water-saturated lightweight aggregates (LWAs) are used in partial replacement of normal weight aggregate as a source of additional water. LWA is submerged in water prior to concrete mixing to absorb a significant amount of water, which is stored within the LWA particles. Once added to the mix, the water is gradually desorbed and compensates the water losses during hydration. Hence, it counteracts the shrinkage induced. Different ICC mixes are developed in this research using two different sizes of LWA, and supplementary binding materials are used to improve compressive strength. ICC compressive strength and reduced shrinkage attained are presented. ICC mixes developed in this research can be successfully used in pouring highway segments and bridge decks with lower cracks and reduced life cycle cost due to reduced maintenance.     

新型红色有机电致发光材料

红色发光材料一直是有机电致发光中为烯缺的材料,也是电致发光全色显示不可缺少的材料。通过设计和合成得到了一种新型红色电发光材料,（2,3’－二羟基偶氮苯）－（8－羟基喹啉）合铝（Ⅲ）（Al（azb-q））,该材料为一种铝的金属络合物,含有两种配体：8－羟基喹啉和2,2’－二羟基偶氮苯。实验证明,该材料具有较高的热稳定性较好的成膜特性,同时材料本身具有一定的电了传输能力。电致发光器件证实了该材料的红色发光特性和良好色度学性质。     

A novel material for grounding resistance reduction agent

Abstract

Basic oxygen furnace slag is a major by‐product of steel‐manufacturing plants, yet is often wasted. Over one million metric tons of basic oxygen furnace slag are generated annually. Recycled basic oxygen furnace slag is generally used in the cement industry, road construction and agriculture. The disposal of large amounts of basic oxygen furnace slag is a big problem for both steel‐makers and government agencies. However, the recycling of basic oxygen furnace slag still faces numerous technical, economical and environmental challenges. This study proposes using basic oxygen furnace slag as the main material in a grounding resistance reduction agent. Adding different proportions of water, cement and salt, the resistivity and clot strength of grounding resistance reduction agent was considered to find an effective combination. The effectiveness of the identified combination in reducing grounding resistance was experimentally verified.     

A novel hybrid carbon material

Both fullerenes and single-walled carbon nanotubes (SWNTs) exhibit many advantageous properties. Despite the similarities between these two forms of carbon, there have been very few attempts to physically merge them. We have discovered a novel hybrid material that combines fullerenes and SWNTs into a single structure in which the fullerenes are covalently bonded to the outer surface of the SWNTs. These fullerene-functionalized SWNTs, which we have termed NanoBuds, were selectively synthesized in two different one-step continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs during CO disproportionation. The field-emission characteristics of NanoBuds suggest that they may possess advantageous properties compared with single-walled nanotubes or fullerenes alone, or in their non-bonded configurations.     

A new method of producing high strength oil palm shell lightweight concrete

This paper presents a new method to produce high strength lightweight aggregate concrete (HSLWAC) using an agricultural solid waste, namely oil palm shell (OPS). This method is based on crushing large old OPS. Crushed OPS are hard and have a strong physical bond with hydrated cement paste. The 28 and 56 days compressive strength achieved in this study were about 53 and 56 MPa, respectively. Furthermore, it was observed that it was possible to produce grade 30 OPS concrete without the addition of any cementitious materials. Compared to previous studies, significantly lower cement content was used to produce this grade of concrete. Unlike OPS concrete incorporating uncrushed OPS aggregate, this study found that there is a strong correlation between the short term and 28-day compressive strength.     

Monolithic lightweight concrete masonry for multi‐storey apartment buildings

Affordable living space has become one of the main talking points in Germany next to the threat of climate change. The SMEs of the German lightweight concrete industry offer regional masonry solutions for detached, semi‐detached, and terraced houses as well as multi‐storey apartment buildings. Particularly in densely populated urban centres, the need for multi‐storey apartment buildings arises constantly. In the following the performance of monolithic lightweight concrete masonry will be described and compared with the relevant requirements for multi‐storey apartment buildings. It will be demonstrated that masonry with supposedly low compressive strength can still fulfil all requirements. Of particular significance here are the external wall‐slab junctions.