Modeling mechanical performance of lightweight concrete containing silica fume exposed to high temperature using genetic programming

In this study, the mechanical performance of lightweight concrete exposed to high temperature has been modeled using genetic programming. The mixes incorporating 0%, 10%, 20% and 30% silica fumes were prepared. Two different cement contents (400 and 500 kg/m³) were used in this study. After being heated to temperatures of 20 °C, 200 °C, 400 °C and 800 °C, respectively, the compressive and splitting tensile strength of lightweight concrete was tested. Empirical genetic programming based equations for compressive and splitting tensile strength were obtained in terms of temperature (T), cement content (C), silica fume content (SF), pumice aggregate content (A), water/cement ratio (W/C) and super plasticizer content (SP). Proposed genetic programming based equations are observed to be quite accurate as compared to experimental results.     

Influence of fly ash on strength and sorption characteristics of cold-bonded fly ash aggregate concrete

Cold-bonded fly ash aggregate concrete with fly ash as part of binder or fine aggregate facilitates high volume utilization of fly ash in concrete with minimum energy consumption. This paper investigates the influence of fly ash on strength and sorption behaviour of cold-bonded fly ash aggregate concrete due to partial replacement of cement and also as replacement material for sand. While cement replacement must be restricted based on the compressive strength requirement at desired age, replacement of sand with fly ash appears to be advantageous from early days onwards with higher enhancement in strength and higher utilization of fly ash in mixes of lower cement content. Microstructure of concrete was examined under BSEI mode. Replacement of sand with fly ash is effective in reducing water absorption and sorptivity attributable to the densification of both matrix and matrix–aggregate interfacial bond. Cold-bonded fly ash aggregate concrete with a cement content of 250 kg/m³, results in compressive strength of about 45 MPa, with a total inclusion of around 0.6 m³ of fly ash in unit volume of concrete.     

Mix proportion of high-strength,roller-compacted,latex-modified rapid-set concrete for rapid road repair

In this study, we optimized a blend of high-strength, roller-compacted, latex-modified rapid-set concrete (RCLMC) that can be re-opened to traffic after 4 h. To this end, we tested several variables in laboratory experiments, including hardening acceleration agents, cement type, latex addition, and CSA admixture ratios. The target compressive strength was 21 MPa after 4 h. A mixture of Type III cement to CSA admixture at 235:165 kg/m³ (400 kg/m³ total binder) and 23.5 kg/m³ latex (10% of the cement weight) achieved the target compressive strength and was the most economically efficient.     

Characteristics of mortar and concrete containing fine aggregate manufactured from recycled waste polyethylene terephthalate bottles

This paper presents the development of lightweight aggregate concrete using fine aggregate that is manufactured from recycled waste polyethylene terephthalate (PET) bottles. Investigations on waste PET lightweight aggregate concrete included three phases: examination of the properties of waste PET lightweight aggregates (WPLA), analysis of the properties of mortar when WPLA was used as fine aggregate, and analysis of the properties of concrete when WPLA was used as fine aggregate. The results of the first phase showed that the WPLA had a density of 1390 kg/m³, a water absorption of 0% and a bulk density of 844 kg/m³. WPLA fineness modulus (F.M.), however, was 4.11, which is higher than the F.M. of river sand. This is because the WPLA was single graded. The results of the second phase showed that for the mortar, in which the WPLA was used as a fine aggregate, the flow value increased, while the compressive strength decreased proportionally to the addition of WPLA with elapsed time. In addition, the amount of water absorption by unit area was higher than for the control mortar (without WPLA) when the WPLA content was either 40% or 60%. For the third phase, the results showed that the slump of the WPLA concrete increased as the WPLA content increased regardless of the water-cement ratio (W/C). In comparison to the control concrete, the 28-day WPLA concrete compressive strength decreased by 5%, 15% and 30%, with an increase of WPLA content of 25%, 50% and 75%, respectively. In addition, for a W/C of 0.49, the structural efficiency (compressive strength/density ratio) of the concrete containing 25% of WPLA was higher than that for the control concrete.     

Oil palm shell as a lightweight aggregate for production high strength lightweight concrete

In Malaysia, oil palm shell (OPS) is an agricultural solid waste originating from the palm oil industry. In this investigation old OPS was used for production of high strength lightweight concrete (HSLC). The density, air content, workability, cube compressive strength and water absorption were measured. The effect of five types of curing conditions on 28-day compressive strength was studied. The test results showed that by incorporating limestone powder and without it, it is possible to produce the OPS concretes with 28-day compressive strength of about 43–48 MPa and dry density of about 1870–1990 kg/m³. The compressive strength of OPS HSLC is sensitive to the lack of curing. The water absorption of these concretes is in the range of good concretes.     

Genetic programming based formulation for fresh and hardened properties of self-compacting concrete containing pulverised fuel ash

Self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact without any segregation and blocking. Elimination of the need for compaction leads to better quality concrete and substantial improvement of working conditions. This investigation aimed to show possible applicability of genetic programming (GP) to model and formulate the fresh and hardened properties of self-compacting concrete (SCC) containing pulverised fuel ash (PFA) based on experimental data. Twenty-six mixes were made with 0.38 to 0.72 water-to-binder ratio (W/B), 183–317 kg/m³ of cement content, 29–261 kg/m³ of PFA, and 0 to 1% of superplasticizer, by mass of powder. Parameters of SCC mixes modelled by genetic programming were the slump flow, JRing combined to the Orimet, JRing combined to cone, and the compressive strength at 7, 28 and 90 days. GP is constructed of training and testing data using the experimental results obtained in this study. The results of genetic programming models are compared with experimental results and are found to be quite accurate. GP has showed a strong potential as a feasible tool for modelling the fresh properties and the compressive strength of SCC containing PFA and produced analytical prediction of these properties as a function as the mix ingredients. Results showed that the GP model thus developed is not only capable of accurately predicting the slump flow, JRing combined to the Orimet, JRing combined to cone, and the compressive strength used in the training process, but it can also effectively predict the above properties for new mixes designed within the practical range with the variation of mix ingredients.     

Experimental investigations on the influence of paste composition and content on the properties of Self-Compacting Concrete

The aim of this paper is to investigate the influence of paste composition and paste volume on the fresh and hardened properties of Self-Compacting Concrete. Nineteen SCC mixtures were investigated for different paste composition and paste volume. Fresh concrete tests such as slump flow, J ring, and V funnel test were performed; hardened concrete tests were limited to compressive strength. The results revealed that slump flow and J ring flow increased with increase in paste volume. A simple empirical equation was proposed for the determination of the paste volume for the required slump flow of SCC. Compressive strength of the different SCC mixtures ranged between 20 MPa and 70 MPa.     

Damage to cement concrete pavements due to exposure to organic compounds in a cold region

Pop-out and disaggregation of aggregate in a 1-year old cement concrete pavement originally mixed with air-entraining (AE) water-reducing agent was observed after the pavement had been exposed to ethylene glycol based snow-melting agent on the surface in the winter. The study used: gas chromatography–mass spectrometry (GC–MS) tests, ¹H Nuclear Magnetic Resonance (NMR) tests, X-ray fluorescence analysis, emission spectral analysis (ICP), elution tests in anion type surfactant solution conducted for mortar and aggregate taken from the cement concrete where pop-out had occurred, as well as samples made by cement paste in the laboratory. Tests of the tensile strength, thermal-stress, and three-dimensional crack analysis by micro-focus computerized tomography (CT) scanner were conducted for specimens (2.5 × 2.5 × 10 cm) taken from the cement concrete where pop-out had occurred and with cement concrete samples made in the laboratory. Microscope observations and Electron Probe Micro Analyzer (EPMA) analysis were conducted for thin samples (2.5 × 2.5 cm and 20 μm thick) taken from the cement concrete where pop-out had occurred. The tests results showed that organic compounds contained in the cement reacted with the cement during the hardening process, generating cracks and gel in the cement paste. It was established that these caused the pop-out of the aggregate, together with the effects of the ethylene glycol based snow-melting agent that the cement concrete had been exposed to. No pop-out or disaggregation of aggregate were found in cement concrete at a repaired section, at the same location, with aggregate of low absorbing water ratio in this cold region and in place for 2 years.     

Production of non-constructive concrete blocks using contaminated soil

In this research, a heavily contaminated humus-rich peat soil and a lightly contaminated humus-poor sand soil, extracted from a field location in the Netherlands, are immobilized. These two types of soil are very common in the Netherlands. The purpose is to develop financial feasible, good quality immobilisates, which can be produced on large scale.To this end, two binder combinations were examined, namely slag cement with quicklime and slag cement with hemi-hydrate. The mixes with hemi-hydrate proved to be better for the immobilization of humus rich soils, having a good early strength development. The heavily contaminated soil with 19% humus (of dm) could not be immobilized using 398 kg slag cement and 33 kg quicklime per m³ concrete mix (binder = 38.4% dm soil). It is possible to immobilize this soil using 480 kg binder (432 kg slag cement, 48 kg quicklime) per m³ of mix (58.2% dm). An alternative to the addition of extra binder (slag cement with quicklime) is mixing the soil with sand containing particles in the range of 0–2 mm. This not only improved the compressive strength of the immobilisates, but also reduced the capillary absorption. All the mixes with the lightly contaminated soil were cost-effective and suitable for production of immobilisates on a large scale. These mixes had good workability, a good compressive strength and a low capillary absorption. The leaching of all mixes was found to be much lower than allowed by the regulations. Given these results, the final mixes in the main experiment fulfilled all the financial and technical objectives.     

A study of the workability and compressive strength characteristics of corn cob ash blended cement concrete

The study investigated the workability and compressive strength characteristics of corn cob ash (CCA) blended cement concrete. Nine classes of CCA-blended cements were employed with the CCA content ranging from 0% to 25%. The 0% CCA replacement involved the use of normal ordinary Portland cement and it served as the control. The mix proportions of cement:sand:granite used were 1:1½:3, 1:2:4 and 1:3:6 with 0.5, 0.6 and 0.7 water-to-cement ratios, respectively. The concrete cubes were tested at the curing ages of 3, 7, 28, 60, 120, and 180 days. Slump and compacting factor tests were carried out to check the effect of CCA on the workability of concrete. The results showed that the concrete slump and compacting factor decreased as the CCA content increased indicating that concrete becomes less workable (stiff) as the CCA percentage increases. The compressive strength of CCA-blended cement concrete was lower than the control at early ages, but improves significantly, and outperforms the control at later ages (120 days and above). The optimum compressive strength of 57.10 N/mm², 40.30 N/mm² and 28.07 N/mm² for 1:11/2:3, 1:2:4 and 1:3:6 mix proportions, respectively at 180 days were obtained at 8% CCA replacement level. It was concluded that only up to 8% CCA substitution is adequate where the blended cement is to be used for structural concrete.     

Lightweight concretes of activated metakaolin-fly ash binders,with blast furnace slag aggregates

This work investigated geopolymeric lightweight concretes based on binders composed of metakaolin with 0% and 25% fly ash, activated with 15.2% of Na₂O using sodium silicate of modulus SiO₂/Na₂O = 1.2. Concretes of densities of 1200, 900 and 600 kg/m³ were obtained by aeration by adding aluminium powder, in some formulations lightweight aggregate of blast furnace slag was added at a ratio binder:aggregate 1:1; curing was carried out at 20 and 75 °C. The compressive and flexural strength development was monitored for up to 180 days. The strength diminished with the reduction of the density and high temperature curing accelerated strength development. The use of the slag had a positive effect on strength for 1200 kg/m³ concretes; reducing the amount of binder used. The thermal conductivity diminished from 1.65 to 0.47 W/mK for densities from 1800 to 600 kg/m³. The microstructures revealed dense cementitious matrices conformed of reaction products and unreacted metakaolin and fly ash. Energy dispersive spectroscopy and X-ray diffraction showed the formation of amorphous silicoaluminate reaction products.     

Water absorption,permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete

This paper presents an experimental study to evaluate effect of cumulative lightweight aggregate (LWA) content (including lightweight sand) in concrete [water/cement ratio (w/c) = 0.38] on its water absorption, water permeability, and resistance to chloride-ion penetration. Rapid chloride penetrability test (ASTM C 1202), rapid migration test (NT Build 492), and salt ponding test (AASHTO T 259) were conducted to evaluate the concrete resistance to chloride-ion penetration. The results were compared with those of a cement paste and a control normal weight aggregate concrete (NWAC) with the same w/c and a NWAC (w/c = 0.54) with 28-day compressive strength similar to some of the lightweight aggregate concrete (LWAC). Results indicate that although the total charge passed, migration coefficient, and diffusion coefficient of the LWAC were not significantly different from those of NWAC with the same w/c of 0.38, resistance of the LWAC to chloride penetration decreased with increase in the cumulative LWA content in the concretes. The water penetration depth under pressure and water sorptivity showed, in general, similar trends. The LWAC with only coarse LWA had similar water sorptivity, water permeability coefficient, and resistance to chloride-ion penetration compared to NWAC with similar w/c. The LWAC had lower water sorptivity, water permeability and higher resistance to chloride-ion penetration than the NWAC with similar 28-day strength but higher w/c. Both the NWAC and LWAC had lower sorptivity and higher resistance to chloride-ion penetration than the cement paste with similar w/c.     

Influences of mixture composition on properties and freeze–thaw resistance of RCC

The paper reports a series of lab investigations carried out on roller compacted concrete (RCC) mixtures containing a wide range of cement contents (100 and 450 kg/m³). The key objectives were to appreciate the effects of variations in the cement content and air entrainment on basic physical, mechanical properties and freeze–thaw (F–T) resistances of RCC mixtures. The Vebe consistency, moisture–density relations, water absorption, permeable voids, compressive strength, and F–T resistances of comparable mixes were evaluated. Physical and mechanical properties indicated a significant deviation from the behavior shown by conventional concrete. Air entrainment was found to be affecting the strength and F/T durability of the mixes. Further analysis shows wide range applications of RCC in various pavement applications.     

Effects of steel fiber addition on mechanical properties of concrete and RC beams

C20 and C30 classes of concrete are produced each with addition of Dramix RC-80/0.60-BN type of steel fibers (SFs) at dosages of 0, 30, 60 kg/m³, and their compressive strengths, split tensile strength, moduli of elasticity and toughnesses are measured. Nine reinforced concrete (RC) beams of 300 × 300 × 2000 mm outer dimensions, designed as tension failure and all having the same steel reinforcement, having SFs at dosages of 0, 30, 60 kg/m³ with C20 class concrete, and nine other RC beams of the same peculiarities with C30 class concrete again designed as tension failure and all having the same reinforcement are produced and tested under simple bending. The load versus mid-span deflection relationships of all these RC and steel-fiber-added RC (SFARC) beams under simple bending are recorded. First, the mechanical properties of C20 and C30 classes of concrete with no SFs and with SFs at dosages of 30 and 60 kg/m³ are determined in a comparative way. The flexural behaviours and toughnesses of RC and SFARC beams for C20 and C30 classes of concrete are also determined in a comparative way. The experimentally determined (mid-section load)–(SFs dosage) and (toughness)–(SFs dosage) relationships are given to reveal the quantitative effects of concrete class and SFs dosage on these crucial properties.     

The properties of concrete made with fine dune sand

This paper presents the results of a study that investigated the properties of concrete made with dune sand. Different control concrete mixtures using ordinary Portland cement (OPC) with a minimum design compressive strength of 40 N/mm² were prepared. The amount of fine aggregates constituted about 36% by weight of all the aggregates. The workability ranged from low of 16 mm to a high of 122 mm. For each control mix, other mixtures were prepared in which the fine aggregates were replaced by different percentages of dune sand ranging from 10% to 100%. The effect of dune sand on the workability, compressive strength, tensile strength, modulus of elasticity and initial surface absorption test (ISAT) was studied. Experimental results show an improvement in the workability of concrete when fine aggregates were partially replaced by dune sand. An increase in slump was measured with increase in dune sand content. However, at high dune sand contents (above 50%); the slump starts to decrease with an increase in dune sand. Generally, the strength values decrease with increase in dune sand replacement. The strength loss was not found considerable as the maximum reduction was less than 25% when fine aggregates were fully replaced by dune sand. The absorption characteristics of concrete made with OPC as measured by the (ISAT) generally increased with higher dune sand contents.     

Effect of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete

The main objective of this study is to provide more data on the effects of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete. In the experimental program, mixtures were prepared by partially replacing natural aggregate by expanded perlite and as a result, unit weights of lightweight concretes in fresh state varied between 700 and 2000 kg/m³. Water to cement ratio was kept constant in all mixtures. Compressive strength, modulus of elasticity, water absorption and capillarity coefficient of the mixtures were determined. Thermal conductivity of the specimens was also obtained. Test results show that the compressive strength and modulus of elasticity decreases with increasing in perlite content. Water absorption and sorptivity coefficient, however, increase with the higher perlite contents. The test results indicate that the thermal conductivity is substantially improved with the use of perlite and a strong relationship between thermal conductivity and unit weight is obtained.     

Lightweight properties and pore structure of foamed material made from sewage sludge ash

Pore structure significantly affects the lightweight characteristics and thermal performance of materials. Therefore, in this study, sewage sludge ash (SSA) was used to make lightweight materials. Physical and chemical properties, and how the mixing proportions affected the foaming behavior were investigated, including the lightweight characteristics and pore structure of the materials produced. The experiments showed that the minimum required cement amount was determined by the compressive strength of the sewage sludge ash foamed material (SSAFM), not its alkali content. The hydration of cement and SSA mainly generated pores with diameters of less than 0.1  μm, but cement added with metallic aluminum powder produced pores with diameters larger than 10  μm. The addition of SSA increased the volume of pores smaller than 10  μm. The thermal conductivity of SSAFM was between 0.084 and 0.102 W/m K. Therefore, SSA could be used as the lightweight filler and heat-insulating material.     

Effects of fineness of cement on polynaphthalene sulfonate based superplasticizer–cement interaction

The effects of fineness of portland cement procured from six different Turkish cement plants, on superplasticizer/cement interaction were investigated. CEM I 42.5 type portland cements (PC) were ground into different finenesses ranging from 280 to 550 m²/kg Blaine values. The effects of PC fineness on initial fluidity and fluidity loss of superplasticized cement paste were evaluated. It was found that increasing the Blaine fineness of incompatible cement up to a certain level reduced the viscosity of cement pastes but had no marked effect on the yield stress of the paste mixtures. Nevertheless, flow loss and also saturation point at 60 min increased with increasing the cement fineness. In other words, pastes with lower viscosity can be produced by using finer cement and more superplasticizer.     

Analytical and experimental studies on composite slabs utilising palm oil clinker concrete

The utilisation of waste materials in the construction industry is an effective way to sanitise the environment and reduces the cost of construction. In this research, palm oil clinker (POC) aggregates was used to fully replace normal aggregates to produce structural lightweight concrete. This concrete was used in the construction of composite slabs with profiled steel sheet. A total of eight full scale composite slabs, six palm oil clinker concrete (POCC) slabs and two conventional concrete slabs were constructed and tested in accordance to Eurocode 4: Part 1.1 and BS 5950: Part 4: 1994. Two shear spans were used, 450 mm for short shear span and 900 mm for long shear span. The structural behaviour of the slabs was investigated and compared. The horizontal shear-bond strength between the concrete and the steel was determined according to two methods; m–k and partial shear connection methods. Test results show that the structural behaviour and the horizontal shear-bond strength of the POCC slabs are nearly similar to the conventional concrete slabs. The mechanical interlock (m) and the friction (k) between the steel and the concrete are 117.67 N/mm² and 0.0973 N/mm², respectively and the design horizontal shear-bond strength using m-k and PSC methods is 0.248 N/mm² and 0.215 N/mm², respectively. The difference between the two methods is 13.3%. POCC is therefore suitable to be used for structural applications with a reduction in weight of 18.3% compared to conventional concrete composite slabs.     

A comparative experimental investigation of concrete,reinforced-concrete and steel-fibre concrete pipes under three-edge-bearing test

Three-edge-bearing and crack size measurement tests were carried out on plain concrete, reinforced-concrete, and steel-fibre concrete pipes of 500 mm diameters. The average three-edge-bearing strength and crack size of steel-fibre concrete pipes having steel fibres of RC80/60-BN type at a dosage of 25 kg/m³ turned out to be 82% greater and 47% smaller than those of plain concrete pipes, and 6% greater and 15% smaller than those of reinforced-concrete pipes, respectively. Tests on those steel-fibre concrete pipes having a steel fibres dosage of 40 kg/m³ revealed that a steel fibres dosage of 25 kg/m³ seems to be close to optimum because a 60% increase in the amount of steel fibres engenders only minor improvements. By these findings, steel-fibre concrete pipes are more economical than and mechanically and physically superior to reinforced-concrete pipes.