A preliminary study of reservoir sludge as a raw material of inorganic polymers

The feasibility of using calcined reservoir sludge as a raw material of inorganic polymers is evaluated by conducting a series of microstructural and mechanical tests. The reservoir sludge particles in Taiwan containing aluminosilicate minerals were first calcined at various high temperatures ranging from 500 °C to 900 °C to enhance the subsequent alkali-activated reaction and polycondensation for making an inorganic polymer. Then, the change of crystalline structure of calcined reservoir sludge particles due to dehydroxylation at high temperatures was characterized by using FTIR and XRD methods. Furthermore, uncalcined and calcined reservoir sludge particles were separately mixed with an alkaline activating solution to produce inorganic polymers and their compressive strengths were measured. From the variations of crystalline structure and compressive strength, an optimum calcination temperature for reservoir sludge is obtained. The effect of fineness of reservoir sludge particles on the compressive strength of inorganic polymers is also discussed.     

Multiaxial tensile–compressive strengths and failure criterion of plain high-performance concrete before and after high temperatures

Multiaxial tensile–compressive tests were performed on 100 mm × 100 mm × 100 mm cubic specimens of plain high-performance concrete (HPC) at all kinds of stress ratios after exposure to normal and high temperatures of 20, 200, 300, 400, 500, and 600 °C, using a large static–dynamic true triaxial machine. Friction-reducing pads were three layers of plastic membrane with glycerine in-between for the compressive loading plane; the tensile loading planes of concrete samples were processed by attrition machine, and then the samples were glued-up with the loading plate with structural glue. The failure mode characteristic of specimens and the direction of the crack were observed and described, respectively. The three principally static strengths in the corresponding stress state were measured. The influence of the temperatures, stress ratios, and stress states on the triaxial strengths of HPC after exposure to high temperatures were also analyzed respectively. The experimental results showed that the uniaxial compressive strength of plain HPC after exposure to high temperatures does not decrease completely with the increase in temperature, the ratios of the triaxial to its uniaxial compressive strength depend on brittleness–stiffness of HPC after different high temperatures besides the stress states and stress ratios. On this basis, the formula of a new failure criterion with the temperature parameters under multiaxial tensile–compressive stress states for plain HPC is proposed. This study is helpful to reveal the multiaxial mechanical properties of HPC structure enduring high temperatures, and provides the experimental and theory foundations (testing data and correlated formula) for fire-resistant structural design, and for structural safety assessment and maintenance after fire.     

Characterization of concrete blocks containing petroleum-contaminated soils

This paper presents the results of a study on the potential use of petroleum-contaminated soil (PCS) in the manufacturing of concrete blocks. PCS was obtained from Fahud asset area in northern Oman, where contaminated soils are typically transported for treatment. Hollow blocks of size 400 × 200 ×200 mm, widely used in Oman, were manufactured with a mix proportion of 1:2:4:0.8 for cement, coarse aggregate, sand, and water, respectively. The coarse aggregate had a 10 mm maximum aggregate size. PCS was subjected to the toxicity characteristic leaching procedure (TCLP). The chemical analysis of the extract indicated that the concentrations of metals and organic compounds did not exceed the maximum contaminant levels set by USEPA for TCLP extracts. Different mixes were prepared by replacing the sand with PCS with percentages up to 80% by sand weight in the mix. Five different tests were conducted on the concrete blocks: density, compressive strength, absorption, compressive strength of a masonry column, and thermal conductivity. The compressive strength test was conducted after 14 and 28 days of curing. The other tests were performed after 28 days of curing. Results indicated that PCS can be used with a replacement percentage up to 60% to produce concrete blocks meeting the Omani Standard specifications. The results also indicate potential deterioration when more than 60% PCS are used.     

Shrinkage characteristics of high-strength concrete for large underground space structures

This study forms part of a research project that was carried out on the development and application of high-strength concrete for large underground spaces. In order to develop 50 MPa high-strength concrete, eight optimal mixtures with different portions of fly ash and ground granulated blast furnace slag, which make the pozzolanic reaction, were selected. For assessments of shrinkage characteristics, free shrinkage tests with prismatic specimens and shrinkage crack tests were performed. The compressive strength was more than 30 MPa at 7 days, and stable design strength was acquired at 28 days. High-strength concrete containing blast furnace slag shows large autogenous shrinkage, while large shrinkage deformations and cracks will occur when mixtures are replaced with large volumes of cementitious materials. Hence, for these high-strength concrete mixtures, the curing conditions of initial ages that affect the reaction of hydration and drying effects need to be checked.     

Parameter optimization on compressive strength of steel fiber reinforced high strength concrete

This paper illustrates parameter optimization of compressive strength of steel fiber reinforced high strength concrete (SFRHSC) by statistical design and analysis of experiments. Among several factors affecting the compressive strength, five parameters that maximize all of the responses have been chosen as the most important ones as age of testing, binder type, binder amount, curing type and steel fiber volume fraction. Taguchi analysis techniques have been used to evaluate L₂₇ (3¹³) Taguchi’s orthogonal array experimental design results. Signal to noise ratio transformation and ANOVA have been applied to the results of experiments in Taguchi analysis. The confirmation runs were conducted for the optimal parameter level combination, which is obtained from the results of the above methodologies. The maximum compressive strength has been observed as around 124 MPa. By using the optimal parameter level combination, the direct tensile strength and flexural strength tests have been conducted. The mean values at the age of 28 days are obtained as 7.5 MPa and 13 MPa respectively. In this study, it is clearly demonstrated that all main factors except steel fiber significantly contribute to the compressive strength of steel fiber reinforced high strength concrete, yet age and binder type are the most significant contributors.     

Critical embedment length and bond strength of fully encapsulated rebar rockbolts

A series of rock bolt pull tests were carried out in the laboratory to determine the critical embedment length of a specific type of fully cement-grouted rebar bolt. The rebar bolt is 20 mm in diameter, and it is widely used in underground excavations in Norway. Three water-cement (w/c) ratios were used in the tests. It was discovered that the critical embedment length of the rock bolts was approximately 25 cm for the water-cement ratio 0.40 (the corresponding uniaxial compressive strength (UCS) of the grout is 37 MPa), 32 cm for the ratio 0.46 (UCS 32 MPa), and 36 cm for the ratio 0.50 (UCS 28 MPa), for the specific type of cement, Rescon zinc rock bolt cement. It was found that the bond strength of the rock bolt is not a constant but is related to the embedment length. The bond strength was linearly proportional to the UCS of the grout.     

Mechanical characterisation of traditional adobes from the north of Spain

Mud is one of humankind’s oldest construction materials. The paper presents a technical study of straw-stabilized adobe, prepared in the traditional manner using wooden frames and compacting the mixture manually. The mud is selected from a specific area in the province of León (Spain) where adobes had been employed traditionally from long years ago using two different proportions of straw: 25% and 33% of total volume. The laboratory tests have followed the standard EN protocols. The different tests developed were of two types: for the natural soil granulometric analysis, relative density and Atterberg limits were made; for the adobes the following were done: shrinkage during drying, density, compressive and flexural strength.Results show an average compressive strength of 3.8 N/mm² and an average flexural strength of 0.68 N/mm², so it can be stated that traditional adobes can be used as an adequate construction material.     

Correlations among mechanical properties of steel fiber reinforced concrete

In this paper, applicability of previously published empirical relations among compressive strength, splitting tensile strength and flexural strength of normal concrete, polypropylene fiber reinforced concrete (PFRC) and glass fiber reinforced concrete (GFRC) to steel fiber reinforced concrete (SFRC) was evaluated; moreover, correlations among these mechanical properties of SFRC were analyzed. For the investigation, a large number of experimental data were collected from published literature, where water/binder ratio (w/b), steel fiber aspect ratio and volume fraction were reported in the general range of 0.25–0.5, 55–80 and 0.5–2.0%, respectively, and specimens were cylinders with size of Φ 150 × 300 mm and prisms with size of 150 × 150 × 500 mm. Results of evaluation on these published empirical relations indicate the inapplicability to SFRC, also confirm the necessity of determination on correlations among mechanical properties of SFRC. Through the regression analysis on the experimental data collected, power relations with coefficients of determination of 0.94 and 0.90 are obtained for SFRC between compressive strength and splitting tensile strength, and between splitting tensile strength and flexural strength, respectively.     

Strengths and flexural strain of CRC specimens at low temperature

Crumb rubber concrete (CRC) is made by adding rubber crumbs into conventional concrete. This study undertakes an experimental study on the cubic compressive strength, axial compressive strength, flexural strength and splitting tensile strength of CRC specimens at both ambient temperature 20 °C and low temperature ?25 °C. The flexural stress–strain responses were also recorded. The averaged size of rubber crumbs used in the study is about 1.5 mm. Four levels of rubber contents are investigated, which are 0%, 5%, 10% and 15% by volume, respectively. The mix design aimed at 40 MPa of compressive strength and 100 mm of slump for all the CRC specimens. The results show that CRC increases its magnitude in strengths when temperature decreases, which is similar to the case of conventional concrete, but still exhibits ductility in low temperature. The conclusion from this study is that CRC may be more beneficial in its application in low temperature environments than in ambient temperature environments.     

High strength characteristics of cement mortar reinforced with hybrid fibres

An experimental study was conducted on high strength mortar reinforced with steel fibres and hybrid fibres consisting of steel fibre, palm fibre and synthetic fibre (Barchip). The inclusion of fibres was maintained at a volumetric fraction of 2%. The compressive strength, splitting tensile strength, static modulus of elasticity, shrinkage, flexural strength, and flexural toughness were determined to study the effect of the hybrid fibres on the properties of high strength cement mortar (HSCM). The results showed that hybridization of fibres in the quantities 1.5% steel fibres + 0.25% palm fibres + 0.25% Barchip fibres, improved the compressive strength and flexural toughness significantly, and also enhanced the splitting tensile strength and flexural strength of the mortar by about 44% and 140%, respectively.     

Effect of fly ash addition on the mechanical properties of tile adhesive

Statistical relationship between various strengths of tile adhesives in which cement or sand was partially replaced with fly ash was studied. A low-lime fly ash was used in five different replacement levels from 5% to 30% by weight of either cement or sand. The tensile adhesion, flexural and compressive strengths of adhesives were determined at 2, 7 and 28 days. In small substitution levels, sand replacement increased the tensile adhesion strength. No strong relationship was found between tensile adhesion strength and flexural or compressive strength of the specimens in which the fly ash was used as sand replacement (r < 0.659). Strong relationship was observed between the same properties when fly ash was used as cement replacement (r > 0.896). Flexural and compressive strength values showed quite strong relationship (r > 0.949). This may be due to the fact that both of these strength values were obtained on the same specimens.     

Influence of calcined kaolin on mortar properties

The use of calcined clay, in the form of metakaolin (MK), as a pozzolanic material for mortar and concrete has received considerable attention in recent years. The present paper describes the results of a research project initiated to study the calcination of local kaolin at various temperatures (650–950 °C) and durations (2, 3 and 4 h) to produce MK with a high pozzolanic activity. The pozzolanic activity was assessed by 28-days compressive strength and hydration heat methods. The maximum identified activity was obtained at 850 °C for 3 h duration. An increase of both hydration heat and compressive strength was obtained when ordinary Portland cement was replaced by 10% MK. The use of ternary blended cement improves the early age and the long-term compressive strength. The durability was also enhanced as better acidic resistance was observed.     

The effect of thiosemicarbazide on corrosion resistance of steel reinforcement in concrete

This study describes a laboratory investigation of the influence of thiosemicarbazide (TSC) on the corrosion of reinforcing steel and the compressive strength of concrete. The effect of TSC on the corrosion resistance of steel reinforced concrete was evaluated by carrying out electrochemical tests in NaCl and NaCl + TSC solutions for 60 days. Polarisation resistance (R_p) values of TSC added reinforced concrete were much higher than those without TSC. Similarly, AC impedance spectra revealed that the resistance of TSC mixed electrodes were also quite higher than those without. The compressive strength of concrete specimens containing TSC was measured and an increase of 20–25% was observed.     

Performance of thermally damaged fibre reinforced concretes

Mechanical characteristics of Fibre Reinforced High Performance Concrete (FR-HPC) subjected to high temperatures were experimentally investigated in this paper. Three different concretes were prepared: a normal strength concrete (NSC) and two High Performance Concretes (HPC1 and HPC2). Fibre reinforced concretes were produced by addition of steel or polypropylene fibres in the above mixtures at dosages of 40 kg/m³ and 5 kg/m³, respectively. A total of nine concrete mixtures were produced and fibres were added in six of them. At the age of 120 days specimens were heated to maximum temperatures of 100, 300, 500 and 700 °C. Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. Reference tests were also performed at air temperature (20 °C). Residual strength of NSC and HPC1 was reduced almost linearly up to 700 °C and 500 °C, respectively whereas the residual strength of HPC2 was sharply reduced up to 300 °C. Explosive spalling was observed on both HPC. Addition of steel fibres increased the residual strength up to 300 °C, but spalling still occurred in HPC1 and HPC2. Such an explosive behavior was not observed when polypropylene fibres were added in the mixtures; however, in this case the residual mechanical characteristics of all concretes were significantly reduced.     

Mechanical properties of natural fibers reinforced sustainable masonry

This research evaluates the physical and mechanical properties of Portland cement masonry blocks reinforced with lechuguilla natural fibers, that were lightened with 2-l bottles of polyethylene terephthalate.A concrete mix was designed for a target compressive strength of 16 MPa at 28 days, and slump of 70 mm. Masonry concrete blocks with dimensions of 730 × 340 × 130 mm were produced for two different fiber lengths (25 and 50 mm) and with fiber contents of 0.25%, 0.50%, 0.75% and 1.0%.Based on the obtained results, it was found that as the aspect ratio decreases the compressive strength increases and that the use of natural fiber (Vf = 0.5–0.75%) improves masonry post-cracking features, showing a ductile behavior and generating a uniform cracking pattern in the longitudinal sides of the blocks.     

Performance of self-compacting concrete containing different mineral admixtures

This paper presents experimental study on the properties of self-compacting concrete (SCC). Portland cement (PC) was replaced with fly ash (FA), granulated blast furnace slag (GBFS), limestone powder (LP), basalt powder (BP) and marble powder (MP) in various proportioning rates. The influence of mineral admixtures on the workability, compressive strength, ultrasonic pulse velocity, density and sulphate resistance of SCC was investigated. Sulphate resistance tests involved immersion in 10% magnesium sulphate and 10% sodium sulphate solutions for a period of 400 days. The degree of sulphate attack was evaluated using visual examination and reduction in compressive strength. The test results showed that among the mineral admixtures used, FA and GBFS significantly increased the workability and compressive strength of SCC mixtures. Replacing 25% of PC with FA resulted in a strength of more than 105 MPa at 400 days. Moreover, the presence of mineral admixtures had a beneficial effect on the strength loss due to sodium and magnesium sulphate attack. On the other hand, the best resistance to sodium and magnesium sulphate attacks was obtained from a combination of 40% GBFS with 60% PC.     

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.     

Effect of GGBFS on time dependent compressive strength of concrete

This paper addresses the compressive strength properties when GGBFS is used to make concrete and discuss in detail the compressive strength development of concrete cubes and cylinders. The uniaxial compression tests have been conducted on these concrete specimens with and without GGBFS at the ages of 3, 7, 28, 56, 90, 150 and 180 days. Experimental values show increasing concrete strength with GGBFS up to 40% but at a higher period of maturity (56 days and more). Sixty percent GGBFS blending, however, shows reduced strength when compared to 40% blending. A comparative study has also been carried out between the experimentally obtained compressive strength and strength predicted by the models given in SP-24 (Indian Standard), ACI-209, CEB-FIP and GL-2000. Based on the experimentally obtained results a strength predicting models has also been proposed for GGBFS based concrete.     

Corrosion of steel reinforcement in concrete of different compressive strengths

Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46 MPa was investigated. Reinforced concrete specimens were immersed in a 3% NaCl solution by weight for 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4 A was applied using portable power supply. Corrosion rate was measured by retrieving electrochemical information of polarization technique. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics.Experimental results showed that corrosion rate of steel bars and bond strength between corroded steel/concrete were dependent on concrete strength and accelerated corrosion period. As concrete strength increased from 20 to 46 MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration caused a slight increase in steel/concrete bond strength, whereas sever corrosion after 7 and 15 days of corrosion acceleration significantly reduced steel/concrete bond strength. Visual and metallographic observation of steel bars removed from concrete samples after testing revealed that the severity of corrosion reactions and reduction of steel bar diameter increased as the corrosion acceleration period increased. Presence of localized corrosion pits as well as severe corrosion grooves of steel bars was confirmed after 7 and 15 days of corrosion acceleration, respectively.     

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.