Parent Concrete Research Articles

Effect of the quality of parent concrete on the properties of high performance recycled aggregate concrete

Abstrac1t This paper presents the experimental results of a study on the effect of the quality of parent concrete (PC) on the properties of recycled aggregates (RAs) that are derived from them, and on the mechanical and durability properties of normal strength and high performance recycled aggregate concrete (NSRAC and HPRAC). PC with strength grades ranging from 30 to 100 MPa was crushed to the size of coarse aggregates (

A new arrangement of galvanic anodes for the repair of reinforced concrete structures

Discrete galvanic anodes are traditionally embedded in the patch repairs of steel reinforced concrete (RC) structures to offer corrosion prevention. This research investigated the performance of galvanic anodes installed in the parent concrete surrounding the patch repair, in order to explore the performance of such a new arrangement and identify its potential for wide-scale application.This arrangement was tested on a RC multi-storey car park and a RC bridge, both suffering from chloride-induced corrosion of the reinforcement. The performance of the anodes was assessed using close-interval potential mapping for 215days after installation. The results indicate that the anodes polarised the steel at a significant distance away from the patch repair interface, up to 600mm in some cases. It illustrates that such an arrangement may be advantageous when repairing RC structures as the corrosion prevention can be targeted at the steel in the surrounding parent concrete, which is traditionally considered to be at higher risk due to incipient anode development.

Acid Treatment Technique for Determining the Mortar Content of Recycled Concrete Aggregates

AbstractThe presence of old cementitious mortar in recycled concrete aggregates (RCA) has been reported to be one of the main factors contributing to a lowering of the performance of concrete made with RCA relative to those made with natural aggregates (NA). This difference in performance has been attributed to the proportion of mortar present in the RCA vis-à-vis the NA used to cast the original parent concrete. Therefore, determining the mortar content might provide an effective means of assessing the overall quality of RCA. Also, as reported in the available literature, it is essential to take into account the amount of mortar present in RCA as part of the total mortar present when designing concrete mixes cast with RCA. However, an easy-to-use standard method for accurately determining the cementitious mortar content of RCA is not available at present. In this study, an acid treatment testing method is proposed to determine the mortar content of RCA. The method is able to remove most, if not all, of the cementitious mortar and takes approximately 24 h to carry out. In addition, the effects of mortar content on properties of RCA including 24-hour water absorption, bulk density, and Los Angeles abrasion resistance were investigated. The effects of the original parent concrete strength on the relationships between mortar content and RCA properties were also investigated. The study was confined to only granitic coarse aggregates.

Effects of the Parent Concrete Properties and Crushing Procedure on the Properties of Coarse Recycled Concrete Aggregates

AbstractFine tuning of concrete recycling processes requires a comprehensive understanding of the overlapping interactions and effects of the various influencing parameters. The most important parameters associated with recycled concrete aggregate (RCA) production that may affect quality and yield include such properties of the parent concrete as the composition, strength and aggregate grading, type of crushers used, number of crushing stages, the size of the RCA particles, and the size reduction sequence. The effects of such parameters overlap and interact with one another and render it impossible for firm conclusions to be drawn on the effects of one parameter in isolation as evidenced by results reported in available literature. The present paper reports on the findings of an experimental study on the concomitant effects of the strength of the parent concrete, size of the natural aggregates used in the parent concrete, and the number of crushing stages on the properties of coarse recycled concrete aggr...

Diagnosing the cause of incipient anodes in repaired reinforced concrete structures

The incipient anode (or halo) effect often occurs on repaired reinforced concrete structures. The diagnosis of this problem is widely reported to be macrocell activity. This diagnosis is based on very limited data. Indeed potential measurements on field structures repaired with proprietary materials have provided data that suggest that macrocell activity is not a cause of incipient anode formation. Alternative mechanisms that may cause incipient anode activity include repair/parent material interface effects, residual chloride contamination within the parent concrete, and/or vibration damage to the steel/parent concrete interface during repair area preparation.

Closed-loop recycling of recycled concrete aggregates

Reduce, reuse and recycle for environment recovery and respect are the key principles of a sustainable construction material. Much research has been conducted regarding the use of recycled concrete aggregates (RCA) in concrete mixes recycled from parent concrete of natural source aggregates, referred here as first generation. Recycling the RCA forming a second loop of recycling concrete is referred here as the second generation of RCA. This study concentrates on the properties of the second generation concrete. The concrete mixes considered in this study are conventional mixes made of 100% natural aggregates (NA), mixes containing up to 20% replacement of NA with RCA, producing first generation concrete and mixes containing up to 20% replacement of NA with aggregates obtained by recycling the first generation concrete (R-RCA), producing the second generation concrete. Properties that have been studied are workability, absorption, compressive and tensile strengths. The results show that the use of RCA and R-RCA has an adverse effect on concrete properties. Results show that the use of up to 20% replacement of NA by RCA or R-RCA instead of NA is allowed for producing concretes of accepted quality. The second generation RCA performed better than the first generation RCA. It is also shown that the closed-loop recycling is possible and advantages maintaining the sustainability of the natural resources and the environment.

AIR CONTENT OF SELF-CONSOLIDATING CONCRETE AND ITS MORTAR PHASE INCLUDING RICE HUSK ASH / ORO KIEKIS SAVITANKIAME BETONE IR JO SKIEDINIO DALYJE SU RYŽIŲ LUKŠTŲ PELENAIS

This paper presents the air content results of self-consolidating concrete (SCC) and its mortar phase including rice husk ash (RHA) as a supplementary cementing material. Moreover, this paper demonstrates a simple technique to determine the dosage of air-entraining admixture (AEA) required for the target air content in SCC. Different SCC mixtures were designed based on the water/binder (W/B) ratios of 0.30–0.50 and design air content of 4–8%. RHA was incorporated in the concretes substituting 0–30% of cement by weight. The mortars were formulated from the mixture proportions of the corresponding parent concretes and tested to determine the air content at various AEA dosages. The effects of W/B ratio and RHA content on the air content of both mortar and concrete were observed. The effect of mortar volume on the air content of concrete was also noticed. Besides, the AEA dosages required for the target air contents of concrete were estimated based on the equivalent mortar air contents. Later the air-entrained SCC mixtures were produced using AEA and tested for the air content. Test results exhibit that the air contents of both mortar and concrete were significantly influenced by the W/B ratio and RHA content. The concrete air content was also greatly influenced by its mortar volume. The AEA dosage increased with lower W/B ratio, higher RHA content, and greater mortar volume for the target air contents. In addition, the actual AEA dosages were consistent with the estimated AEA dosages of the concretes. An excellent correlation was observed between the actual and estimated AEA dosages. The strong correlation suggests that the AEA dosage needed for a target air content in concrete can be determined based on the equivalent air content of its mortar phase. Santrauka Straipsnyje pateikiami oro kiekio nustatymo savitankiame betone (SCC) ir jo skiedinio dalyje su ryžių lukštų pelenais (RHA), naudojamais kaip papildoma cementavimo medžiaga, rezultatai. Be to, pateikiamas paprastas būdas parinkti orą įsiurbiančio priedo (AEA) dozę, siekiant gauti reikalingą oro kiekį SCC. Suprojektuoti skirtingi SCC mišiniai su skirtingu vandens ir rišiklio (W/B) 0,30–0,50 santykiu ir numatytu 4–8 proc. oro kiekiu, RHA buvo dedamas į betoną pakeičiant 0–30 proc. cemento pagal masę. Skiediniai buvo formuojami pagal jiems artimo betono sudėtis ir oro kiekis juose bandomas su skirtingomis AEA dozėmis. Nustatyta W/B santykio ir RHA kiekio įtaka oro kiekiui tiek skiedinyje, tiek betone bei skiedinio tūrio įtaka oro kiekiui betone. Be to, AEA dozės, reikalingos numatytam oro kiekiui betone pasiekti, nustatytos pagal ekvivalentinį oro kiekį skiedinyje. Vėliau SCC mišiniai su orą įsiurbiančiu priedu buvo pagaminti naudojant AEA ir išbandytas juose esantis oro kiekis. Tyrimų rezultatai rodo, kad tiek skiedinį, tiek betono oro kiekį labai veikia W/B santykis ir RHA kiekis. Oro kiekį betone taip pat smarkiai veikia skiedinio tūris. Mažėjant W/B santykiui, didėjant RHA kiekiui ir skiedinio tūriui AEA dozė turi būti didinama norimam oro kiekiui pasiekti. Taip pat faktinės AEA dozės atitiko suskaičiuotas betonų AEA dozes. Tarp faktinių ir suskaičiuotų AEA dozių gauta labai gera koreliacija. Ji rodo, kad AEA dozę, reikalingą numatytam oro kiekiui betone pasiekti, galima skaičiuoti pagal ekvivalentinį oro kiekį šio betono skiedinio dalyje.

Effect of recycled coarse aggregate on concrete compressive strength

The effect of recycled coarse aggregate on concrete compressive strength was investigated based on the concrete skeleton theory. For this purpose, 30 mix proportions of concrete with target cube compressive strength ranging from 20 to 60 MPa were cast with normal coarse aggregate and recycled coarse aggregate from different strength parent concretes. Results of 28-d test show that the strength of different types of recycled aggregate affects the concrete strength obviously. The coarse aggregate added to mortar matrix plays a skeleton role and improves its compressive strength. The skeleton effect of coarse aggregate increases with the increasing strength of coarse aggregate, and normal coarse aggregate plays the highest, whereas the lowest concrete strength occurs when using the weak recycled coarse aggregate. There is a linear relationship between the concrete strength and the corresponding mortar matrix strength. Coarse aggregate skeleton formula is established, and values from experimental tests match the derived expressions.

Deterioration of Bond Integrity between Repair Material and Concrete due to Thermal and Mechanical Incompatibilities

The slant shear test highlighted by British Standard 6319 No. 4 was used to evaluate the bond strength between selected repair materials and parent concrete. Seven resinous and six cementitious repair materials were used to repair fractured specimens. Repaired test specimens were aged by subjecting them to heat-cool cycles that simulated repeated extreme summer day in the southern part of the United States (e.g., Mississippi). The results of thermal cycling showed a strong correlation between the difference in the coefficient of thermal expansions, as well as the difference in elastic moduli, between repair materials and concrete, and the reduction in bond strength. Although resinous materials possessed a higher bond strength to concrete, they showed higher reduction of bond strength than cementitious materials.

Influence of parent concrete on the properties of recycled aggregate concrete

This paper discusses first the properties of recycled aggregates derived from parent concrete (PC) of three strengths, each of them made with three maximum sizes of aggregates. The relative physical and mechanical properties of fresh granite aggregate are discussed. Using these nine recycled aggregates, three strengths of recycled aggregate concrete (RAC) were made and studied. Typical relationship between water–cement ratio, compressive strength, aggregate-cement ratio and cement content have been formulated for RAC and compared with those of PC. RAC requires relatively lower water–cement ratio as compared to PC to achieve a particular compressive strength. The difference in strength between PC and RAC increases with strength of concrete. The relative evaluation of tensile and flexural strengths and modulus of elasticity has also been made.

Relative moisture movement through recycled aggregate concrete

This paper discusses the relative permeation characteristics (volume of voids and water absorption (ASTM C642-97) and sorption) of three strengths of concrete with (i) three maximum sizes of fresh granite aggregates (parent concrete), (ii) recycled concrete aggregates derived from each of three strengths of parent concrete, and (iii) two types of crushed brick aggregates. For a given strength, the volume of voids, water absorption and sorptivity of recycled aggregate concrete (i) reduces with increase in maximum size of aggregate used, (ii) increases with increase in strength of parent concrete from which the recycled aggregate is derived, and (iii) is higher for brick aggregate concrete than for concrete produced with crushed concrete aggregate. The variation in volume of voids, water absorption and sorptivity between parent concrete and recycled aggregate concrete reduces with increase in strength of concrete.

Relative moisture movement through recycled aggregate concrete

This paper discusses the relative permeation characteristics (volume of voids and water absorption (ASTM C642-97) and sorption) of three strengths of concrete with (i) three maximum sizes of fresh granite aggregates (parent concrete), (ii) recycled concrete aggregates derived from each of three strengths of parent concrete, and (iii) two types of crushed brick aggregates. For a given strength, the volume of voids, water absorption and sorptivity of recycled aggregate concrete (i) reduces with increase in maximum size of aggregate used, (ii) increases with increase in strength of parent concrete from which the recycled aggregate is derived, and (iii) is higher for brick aggregate concrete than for concrete produced with crushed concrete aggregate. The variation in volume of voids, water absorption and sorptivity between parent concrete and recycled aggregate concrete reduces with increase in strength of concrete.

Particle size analysis of material removed during CO2 laser scabbling of concrete for filtration design

This article examines the particles formed during optimized laser scabbling of concrete in order to help determine an effective filtration strategy for the process. The laser scabbling technique has been developed for noncontact removal of radioactive contaminated surface concrete layers. Surface layer removal is effected using a high power carbon dioxide laser beam to generate stresses in the substrate (caused by temperature gradients and dehydration) which break up the surface. The material removed will be contaminated with radionuclides and its efficient collection must be ensured to prevent the escape of radioactive contaminated particles. The filtration methods selected depend on the size of the particles produced and transport characteristics in an airflow. The particles removed were examined using a laser diffraction particle sizer (for particles below 80 μm physical diameter) and sieving (above 150 μm physical diameter) to determine the particle size distribution. Scanning electron microscope (SEM) analysis was used to identify the components present. The study found that particles removed were constituents of the parent concrete, there were no signs of melting and a small volume fraction (less than 1%) of sub-100 μm physical particle diameter. Particles with aerodynamic diameters under 100 μm are airborne and those between 1 and 30 μm are inhaled into the thoracic and bronchial tracts and lungs. Efficient filtration is required to capture these particles. However, filtration is difficult in the 0.1–1 μm aerodynamic diameter range, which comprises only 0.02% by volume of the removed material. It is considered that laser scabbling of concrete using this method will produce no additional risks than the use of other surface removal mechanisms.

Compatibility of repair mortars with concrete in a hot-dry environment

Strengthening, maintenance and repair of concrete structures are becoming more recognised in the field of civil engineering. There is a wide range of repair mortars with varying properties, available in the market and promoted by the suppliers, which makes the selection of the most suitable one often difficult. A research programme was conducted at Leeds University to investigate the properties of cementitious, polymer and polymer modified (PMC) repair mortars. Following an earlier publication on the intrinsic properties of the materials, this paper presents results on the compatibility of these materials with concrete. The dimensional stability is used in this study to investigate the compatibility of the repair mortars and the parent concrete. Composite cylindrical specimens (half repair mortar/half concrete) were prepared and used for the measurements of modulus of elasticity and shrinkage. The results of the different combined systems were obtained and compared to those calculated using a composite model. The variations between the measured and calculated values were less than 10%. The paper attempts to quantify the effect of indirect differential shrinkage on the permeability and diffusion characteristics of the different combined systems.

Estimating the potential strength of concrete with prior load history

Recommended procedures in evaluating the results of concrete core testing to establish the estimated in situ cube strength or estimated potential strength of concrete are given in standards and guidance documents. Many factors have been considered to determine their combined influence in the interpretation of the conversion process, from a core strength to an equivalent moulded cube strength. Nonetheless, it is recognized that further research is required to determine the effects of other influencing factors. This experimental investigation examines the effects of different degrees of simulated uniaxial compressive load history within prismatic concrete specimen on the strength of cores drilled in the direction of the load history from different locations of the specimen. The results show that the strength of a core drilled from such parent concrete may be as much as 31·7% lower than that of a similar size core drilled from similar parent concrete which has no prior load history.

Cost-Effective Control of Concrete Quality Using Small Specimens of Mortar Extracted from Concrete

Abstract Based on criticisms of the traditional approach to the control of concrete quality which often relies entirely on 28-day compressive strength assessment, a new approach is proposed which involves monitoring quality in various ways from the time of mixing. The alternatives examined are: recording batch weights to establish W-C ratio, monitoring consistency, analyzing freshly prepared mortar or concrete mixtures to determine water content and cement content, and assessing strength potential by means of autoclave or hot-water curing. On the basis of past case histories, it is concluded that assessment of strength potential must remain the primary assurance of concrete quality, and that the other alternatives can only complement rather than substitute for strength assessment. The techniques proposed for mixture analysis and strength assessment involve testing specimens prepared from a sample of mortar extracted from the parent concrete, on the premise that just about anything that is detrimental to the quality of the concrete will manifest itself in the quality of the extracted mortar. Provided the relationship between mortar and concrete strength is established from trial mixtures or past plant records for the materials in question, it is shown that strength potential can be effectively and routinely assessed using autoclave or hot-water curing of 25 by 50 mm (1 by 2 in.) mortar cylinders, and that water content can likewise be determined from oven drying of small specimens of mortar. The problem of determining cement content with acceptable accuracy and precision is not completely solved either by the wet-sieving technique discussed herein or by any of the other available physical or chemical techniques. The techniques proposed for strength assessment and mixture analysis offer considerable potential for cost savings in concrete quality control because of the small size of the facilities needed, their consequent portability, and their relatively low capital and operating costs compared with the equivalent costs of conventional concrete testing.

Preparation and properties of sulphur-infiltrated autoclaved concrete

Autoclaved concrete specimens were infiltrated with liquid sulphur at 150°C. The rates of sulphur infiltration, the mechanical properties and the durability of the infiltrated specimens were all found to be greatly influenced by the nature of the porosity of the uninfiltrated parent concretes. The size distribtuions of pores in the specimens were found to be controlled by the CaO/SiO 2 (mole) ratio of the binder.