Assessment of shear capacity of adhesive anchors for structures using neural network based model

In this study, an artificial neural network (NN) based explicit formulation for predicting the edge breakout shear capacity of single adhesive anchors post-installed into concrete member was proposed. To this aim, a comprehensive experimental database of 98 specimens tested in shear was used to train and test NN model as well as to assess the accuracy of the existing equations given by American Concrete Institute and prestressed/precast concrete Institute. Moreover, the proposed NN model was compared with another existing model which had been derived from gene expression programming by the authors in a previous study. The prediction parameters utilized for derivation of the model were anchor diameter, type of anchor, edge distance, embedment depth, clear clearance of the anchor, type of chemical adhesive, method of injection of the chemical, and compressive strength of the concrete. The proposed model yielded correlation coefficients of 0.983 and 0.984 for training and testing data sets, respectively. It was found that the predictions obtained from NN agreed well with experimental observations, yielding approximately 5 % mean absolute percent error. Moreover, in comparison to the existing models, the proposed NN model had all of the predicted values in ±20 % error bands while the others estimated up to %160 error

Rheological and fresh properties of self-compacting concretes containing coarse and fine recycled concrete aggregates

In this study, the rheological and fresh properties of self-compacting concrete (SCC) using recycled concrete aggregate (RCA) as both coarse and fine aggregates have been investigated. SCC mixtures were prepared containing natural aggregate replacements at the levels of 0, 50 and 100% for coarse recycled concrete aggregates (CRCA) and in each series of mixtures fine recycled concrete aggregate (FRCA) replacements were varied at the levels of 0, 25, 50, 75 and 100%. In all concrete mixtures, 20% of cement content was replaced with fly ash (FA) and water-to-binder ratio (w/b) was used as 0.32. HerschelBulkley and modified Bingham models were adopted in this paper instead of traditional Bingham model to describe the rheological behaviour of SCC with'RCA indicating a non-linear and shear thickening behaviour due to lower yield stress close to zero. The influence of RCA replacements on the shear thickening behaviour of SCC was explained using the rheological analyses. The slump flow and T-500 time, V-funnel time and L-box height ratio tests were carried out to identify the effects of both CRCA and FRCA utilisations on the fresh properties of SCC. The results reveal that Herschel-Bulkley and modified Bingham models provide well defined rheological representations for SCC with RCA. The self-compactibility characteristics of the concretes are remarkably improved by the replacement levels of CRCA and FRCA used in SCC mixtures. (C) 2016 Elsevier Ltd. All rights reserved

Effect of surface treatment methods on the properties of self-compacting concrete with recycled aggregates

In this experimental study, the adverse effect of old cement-mortar composite on self-compacting concrete (SCC) containing recycled concrete aggregate (RCA) were investigated by means of potential aggregate treatment methods so as to promote the maximum RCA utilisation. Although the limited researches focus on the direct utilisation of untreated RCA in SCC, the hitherto unavailable results to the properties of SCCs containing treated RCAs are presented in this paper. Four alternative aggregate surface treatment methods introduced to RCAs are two-stage mixing approach, pre-soaking in HCl solution, water glass dispersion and cement-silica fume slurry. 100% coarse RCA replacement with the natural aggregate was used in SCC mixes having constant cement dosage, fly ash replacement and water-to-binder ratio. The slump flow and T-500 time, V-funnel time, L-box height ratio, viscosity, compressive and splitting tensile strength, and freeze-thaw cycling tests were carried out to identify the effects of these aggregate treatment methods on the key properties of SCC. Test results reveals that self-compactibility characteristics of the concretes are remarkably affected by surface treatment of RCAs. Moreover, the treatment methods of two stage mixing approach and water glass provide more dense and connected microstructures in SEM analysis leading to significant strength improvements compared to the control SCC. (C) 2014 Elsevier Ltd. All rights reserved

Properties of ultra-high performance fiber reinforced cementitious composites made with gypsum-contaminated aggregates and cured at normal and elevated temperatures

Aggregates in many parts of the Middle East are contaminated with gypsum. Therefore, in this study the effects of using gypsum-contaminated natural sand on the compressive strength and expansion of ultra-high performance fiber reinforced cementitious composites (UHPFRCCs) were investigated over a period of one year. Two groups of UHPFRCCs were designed with binary and ternary cementitious blends of Portland cement, silica fume, and/or ground granulated blast furnace slag. Each group consisted of five mixes with different SO3 contents of between 0.11% and 4.5% by weight of natural sand. For each mix, the samples were either water cured or steam cured over a 48 h period. The microstructure of the cementitious composites was also studied by the SEM-EDX. Besides, some findings of UHPFRCCs were compared to those of Portland cement mortars. Test results indicated that UHPFRCCs showed a strength gain, particularly under steam curing and an insignificant expansion even in the presence of excess sulfates, in contrast to the mortars. (C) 2015 Elsevier Ltd. All rights reserved

The effect of aggregates with high gypsum content on the performance of ultra-high strength concretes and Portland cement mortars

There is an increasing demand to ultra-high strength cement-based materials in the Middle East despite finding fine aggregates with a normal SO3 level is a major challenge. This study was conducted to investigate the effect of increasing gypsum content of natural river sand on the properties of water and steam cured ultra-high strength concretes (UHSCs) and Portland cement mortars. All concrete and mortars were prepared with a w/c ratio of 0.197 and 0.440, respectively; yielding 28-day compressive strength ranges of 120-142 and 43-70 MPa, respectively. The experimental tests were expansion, compressive and splitting tensile strengths, and X-ray diffraction at varying ages. UHSC and mortar exhibited significant difference in resistance to internal sulfate attack. While UHSCs were not significantly affected by increasing gypsum content of sand, the Portland cement mortars deteriorated as seen by a drop in strength, a significant swelling, and the presence of expansive ettringite. (C) 2016 Elsevier Ltd. All rights reserved

Mechanical and fracture characteristics of self-compacting concretes containing different percentage of plastic waste powder

This study addresses the mechanical and fracture properties of self-compacting concretes (SCCs) containing plastic waste (PW) powder in varying amounts used as a cement replacement material. Partial amount of cement was replaced by PW powder at 5%, 10%, 15%, 20% and 25% by weight so as to design six SCC mixtures with a constant slump flow of 700 ± 30 mm, total binder content of 550 kg/m3 and water-to-binder (w/b) ratio of 0.35. Mechanical characteristics of SCCs were tested for compressive and splitting tensile strengths, net flexural strength as well as modulus of elasticity at 28 day. Moreover, failure characteristics of the concrete were monitored via three-point bending test on the notched beams. The findings indicated that mechanical properties of PVC powder modified SCCs decreased while the concretes became less brittle

Durability and Shrinkage Characteristics of Self-Compacting Concretes Containing Recycled Coarse and/or Fine Aggregates

This paper addresses durability and shrinkage performance of the self-compacting concretes (SCCs) in which natural coarse aggregate (NCA) and/or natural fine aggregate (NFA) were replaced by recycled coarse aggregate (RCA) and/or recycled fine aggregate (RFA), respectively. A total of 16 SCCs were produced and classified into four series, each of which included four mixes designed with two water to binder (w/b) ratios of 0.3 and 0.43 and two silica fume replacement levels of 0 and 10%. Durability properties of SCCs were tested for rapid chloride penetration, water sorptivity, gas permeability, and water permeability at 56 days. Also, drying shrinkage accompanied by the water loss and restrained shrinkage of SCCs were monitored over 56 days of drying period. Test results revealed that incorporating recycled coarse and/or fine aggregates aggravated the durability properties of SCCs tested in this study. The drying shrinkage and restrained shrinkage cracking of recycled aggregate (RA) concretes had significantly poorer performance than natural aggregate (NA) concretes. The time of cracking greatly prolonged as the RAs were used along with the increase in water/binder ratio