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Carbon dioxide concentration is steadily increasing in large cities. Consequently, durability evaluation of RC (Reinforced Concrete) structures considering carbonation is becoming a serious issue. Construction joints are used for the effective construction of concrete structures. However, cold joints which are caused by delayed placing and poor surface treatment are vulnerable to shear force and the inflow of carbon dioxide. In this study, an accelerated carbonation test was performed for normal-strength concrete using NPC (Normal Portland Cement) and slag after applying tensile and compressive stresses. The carbonation characteristics were quantified considering the effects of cold joint and the induced stress, and structural analysis was performed using the section laminae approach for a 2-span continuous reinforced concrete T-beam bridge. The service life of top and bottom concretes was evaluated considering the calculated stress, existing carbonation velocity equation, and carbonation function according to the stress. The service life showed a similar trend to that of the applied moment. Changes of 103.6%–64.7% (NPC) and 78.0%–108.8% (slag) were observed on the top surface, whereas changes of 103.8%–65.9% (NPC) and 112.9%–79.6% (slag) were observed on the bottom surface. The service life significantly decreased owing to the increasing carbonation depth for the cold joint in the tension part. This suggests that special care should be taken for cold joints during maintenance.

The present study aims to examine the limitation and significance to develop sustainable lightweight concrete using bottom ash aggregates and preformed foam (LWC-BF). As a positive action for sustainability, ordinary Portland cement (OPC) was replaced by using 50% ground-granulated blast-furnace slag (GGBS) and 20% fly ash (FA), and bottom ash particles were used for entire replacement of natural fine and coarse aggregates. To improve the thermal resistance of concrete, preformed foam was added at the maximum volume fraction of 25%. The test parameters investigated included unit binder content, foam volume fraction, and curing temperature. The different mechanical properties and thermal conductivity for LWC-BF were formulated from the regression analysis using test data. Additionally, the measured compressive strength, thermal conductivity, and air-dried density of LWC-BF were compared with the requirements for precast concrete (PC) insulation panel. Thus, a reliable mixture proportioning for the application to the PC insulation panel could be recommended with the use of unit binder content of 500 kg/m3 and foam volume fraction ranging from 10% to 25%.

This paper proposes an integrated concrete surface treatment with surface enhancement via silicate impregnation and surface spraying with TiO2 (a photocatalyst). In this work, two types of silicate-based materials, sodium alumina silicate (SAS) and colloidal silica (COS) were used. Various tests were carried out to characterize the silicate properties and engineering performance of the impregnated concrete. In addition, the purification performance in concrete sprayed with TiO2 was investigated. Concrete impregnated with silicate and sprayed with TiO2 showed an improvement in the durability and mechanical performance because of the addition of the CSH gel and TiO2 barrier. After impregnation, the TiO2 applied by spraying retained good performance for the removal of acetaldehyde and methyl orange.

The objective of the present study is to provide a databank and comprehensible design equations for the shrinkage strain curve of lightweight aggregate concrete (LWAC) by using artificially expanded bottom ash and dredged soil granules. A total of 25 concrete mixtures were prepared with regard to the parameters of the substitution level of natural sand for lightweight fine aggregates and water-to-cement ratios. Based on the experimental observations, the time function, and 91-day shrinkage strain as a specific point were formulated by introducing the parameter of an equivalent porosity of aggregates to rationally evaluate the shrinkage strain curve of LWAC. Test results showed that the amount of shrinkage strain at 28 days ranged between 39% and 55% of that measured at 210 days, indicating that the acceleratory period was delayed due to the internal curing effect of lightweight aggregates. The shrinkage strains of LWAC decreased in proportion to the equivalent porosity ( P eq ) of aggregates, showing that the decreasing rates of the shrinkage strains ranged between 16% and 36% at 3 days, and 21% and 23% at 180 days when P eq value increased from 21.8% to 42.9%. For the proposed equations, the mean and standard deviation of the normalized root-mean-square error values between experiments and predictions are 0.44 and 0.21, respectively, resulting in a better accuracy than the code models (fib 2010 and EC 2) of which comparisons resulted in high overestimation, especially at an early age.

This study examined the effect of the concrete unit weight on the seismic performance of reinforced concrete columns. Three types of columns all-lightweight aggregate concrete, sand-lightweight aggregate concrete, and normal-weight concrete (NWC) were prepared with different amounts of transverse reinforcement and magnitudes of the applied axial load level. Nine columns were tested to failure under constant axial load and cyclic lateral loads. The axial force–moment interactions of column specimens were compared with the predictions obtained by ACI 318–19 procedure using the equivalent stress block and section lamina approach considering the actual stress–strain relationships of various concrete types. The curvature ductility ratios determined from the columns were compared with the ductility-based design procedure specified in EC 8. Test results showed that the moment capacity of lightweight aggregate concrete (LWAC) columns is lower than that of NWC columns, yielding that the safety of ACI 318–19 procedure slightly decreases for columns with a lower concrete unit weight and under lower applied axial load level. The ductility of columns also decreased with a decrease in concrete unit weight, revealing lower values of displacement ductility ratio and equivalent damping coefficient for LWAC columns than NWC columns. Thus, LWAC columns require more transverse reinforcement to achieve a similar seismic ductility to NWC columns under the same design conditions.

The objective of the present pioneering study is to examine the significance and limitations of the development of new biological coating mortars to protect the substrate of concrete exposed to chemical and microbiological attacks. Acting as a block membrane against the exogenous attack, the glycocalyx that is formed around the cell during bacterial cultivation and growth is introduced in the coating mortars. An inventive immobilization process using expanded vermiculite containing numerous internal pores, and a magnesium potassium phosphate composite (MKPC) as a near-neutral binder were implemented to achieve the preferable environment for growth and survival of bacteria within the hardened mortars. Based on the assessment of the productivity of the glycocalyx of various photosynthetic bacteria, the cultivated bacterium Rhodobacter blasticus in malic acid medium is recommended as a primary strain for the coating of mortars. The setting behavior, compressive strength development, and pH variation of the biological coating materials were evaluated as the replacement level of expanded vermiculite that contained bacterial agents varied from 0 to 10%. The population of bacteria immobilized into the expanded vermiculite and incorporated within the mortars verified that the present approach is practical to achieve the growth environment of bacteria. Overall, the developed biological coating mortar possesses significant potential toward an ideal biomimetic material for concrete structures and their maintenance.

The present study examined the flexural behavior of externally post-tensioned lightweight aggregate concrete (LWAC) beams under symmetrical top one-point, two third-point, and analogous uniform loading systems. With respect to the test parameters, eccentricity of prestressing strands and configuration of deviators for the harped strands varied under different loading conditions. All the test beams had the same geometrical dimension and amount of mild longitudinal bars and prestressing strands. The flexural capacity, stress increase ( Δ f ps ) of the unbonded strands at the ultimate state, and displacement ductility ratio ( μ ) measured in the present beams were compared with those of the internally post-tensioned LWAC one-way members. The comparisons clearly indicated that Δ f ps and μ measured in the externally post-tensioned beams were lower than those of the internally post-tensioned one-way members with the same reinforcing index. This trend was independent of the loading type. Although the design equations for Δ f ps specified in American concrete institute (ACI) provision are conservative in the present beams, the safety level exhibits a significant decrease when compared with the results obtained in the internally post-tensioned LWAC beams. The nonlinear analysis indicates a good agreement for the load–displacement with test results, although a slight overestimation in terms of the flexural strength was observed for beams under an analogous uniform load.

The stress due to volume change causes cracking in concrete, so that construction joint is intentionally prepared for an efficient construction and crack controlling in mass concrete structure. Cold joint means a weak joint area which may occur due to imperfect treatment of pre-placed concrete surface and delayed concrete delivery. Many researches have been performed for a quantitative evaluation of chloride ingress in cold joint concrete, which puts an emphasis on the more rapid penetration of chloride ions. The applied loading condition is one of the major reasons for concrete cracking and it also has a great effect on chloride penetration before the stage of cracking. Steel corrosion in concrete is accelerated when concrete cover has unsound area such as crack and cold joint. Chloride diffusion behavior varies with reduction of porosity and enhancement of hydrates, so called time effect on chloride diffusion. The effect of time and of cold joint on chloride diffusion is an important parameter for quantitative durability design for RC (Reinforced Concrete) structures exposed to various loading conditions. This paper investigates changes in chloride diffusion coefficient in cold joint concrete considering time effect and various loading conditions. Concrete samples with 0.6 of w/b (water to binder) and 40% replacement ratio of GGBFS (Ground Granulated Blast Furnace Slag) were prepared, and the chloride diffusion coefficients were measured for 1 year-cured concrete considering tensile and compressive loading conditions. The results were analyzed with the previous results in 91 days-cured concrete for evaluation of time effect. In the work, the time dependent chloride diffusion behaviors were quantitatively evaluated and discussed considering various effects of GGBFS, tensile and compressive stress levels, and cold joint.

While most recycled aggregates are obtained through the wet-treatment process, the objective of the present study was to examine the effectiveness of a dry-treatment technique for removing the cement pastes attached to recycled aggregates obtained from radioactive waste concrete to improve the dismantling and recycling technologies used in nuclear power plants. The aggregates obtained from the waste concrete were dry-treated with calcination at 600 °C and triturated for 1–12 h. The amount of cement pastes attached to the recycled aggregates was quantitively estimated by immersing the aggregates in 20% sulfuric acid. The water absorption and oven-dry density of the dry-treated recycled coarse aggregates were compared with the quality requirements specified in KS F 2527 and JIS A 5021 for natural aggregates. Based on a regression analysis using the test results, simple equations were formulated to explain the relationships between the amount of attached cement pastes and the water absorption and porosity of the recycled coarse aggregates. The dry treatment involving calcination at 600 °C and 12-h trituration is promising for obtaining recycled coarse aggregates with high quality and a small amount of attached cement pastes.

This study presents the structural potentials of an entire restoration technique proposed for upgrading the strength and ductility of severely damaged non-seismic columns. Three columns were prepared under concentric axial loads to examine the axial load–axial strain relationship of restored columns. Additionally, five columns subjected to a constant axial load and cyclic lateral loads were prepared to ascertain the seismic behavior of the restored columns. To simulate the entire restoration of damaged columns, non-seismic columns were initially tested up to their peak axial capacity or 80% of the flexural strength on the post-peak performance; the longitudinal and transverse reinforcing bars and concrete were then reconstructed after total removal from the initially damaged columns. The test results showed that the axial load–axial strain and lateral load–lateral displacement relationships of the restored columns exhibited pre-peak behavior that was quite similar to that of the initial non-seismic columns, whereas the slope at the post-peak branches significantly slowed down for the former columns in comparison to the latter ones. Thus, the axial and flexural strengths of the restored columns could be conservatively assessed by the procedure recommended in the ACI 318-19 provision. The restored columns displayed axial ductility and flexural displacement ductility ratios comparable to those obtained in columns strengthened using the reinforced concrete (RC) jacket with seismic details that were developed using an approach similar to the proposed restoration technique. Thus, the proposed technique shows significant potential in enhancing the seismic performance of severely damaged non-seismic columns by providing confinement to concrete cores and preventing premature buckling of longitudinal reinforcements.

This study aims to provide databank and comprehensible design equations for the shrinkage strain curve of concrete using bottom ash granules to replace conventional natural sands. We prepared 27 concrete mixtures with various parameters, including the substitution level of natural sand for fine bottom ash aggregates, unit water content, and fine aggregate-to-total aggregate volume ratios. To derive reliable design models to predict the drying shrinkage of concrete using fine bottom ash aggregates, the time function specified in fib 2010 was modified by introducing the parameter of equivalent porosity of aggregates. Moreover, the shrinkage strain values at an age of 91 days were formulated by conducting a regression analysis using test data as a specified reference to determine the ultimate shrinkage strain. The test results showed that the shrinkage strain of concrete is marginally affected by the bottom ash aggregate content but significantly affected by the volume fraction of aggregates and their equivalent porosity. The proposed models are promising for estimating the shrinkage strain response of concrete using fine bottom ash aggregates by considering the restraining action of aggregates.

The objective of the present study is to examine the effect of the water-to-binder ratio (W/B) and the molar ratio (Mmp) of magnesium-to-phosphate on the fluid characteristics, compressive strength development, and pH variation of magnesium potassium phosphate composite (MKPC) mortars. A total of 25 mortar mixes were prepared, with the W/B varying from 20% to 40% and Mmp varying from 3.4 to 30.4. Using the present test data, the compressive strength development of MKPC mortars was empirically formulated, which reflects rapid strength gain. Considering practical qualifications, including a relatively good 28-day compressive strength above 30 MPa, delayed setting time, and a near-neutral pH not exceeding 9.4, it can be recommended that the Mmp and W/B be chosen to be below 5.1 and above 25%, respectively, in the MKPC system. With a decrease in the Mmp value, the peak intensities for struvite-k increased slightly, whereas the peak intensities for unreacted MgO were considerably weakened as the Mmp value fell below 5.1. The total porosity of the MKPC pastes was governed by the macro-capillary pores, implying that the 28-day compressive strength is inversely proportional to the macro-capillaries.

To develop a neutral binder for vegetation concrete, various cementitious materials based on alpha-calcium sulfate hemihydrate (α-CH) were compositionally examined as follows: 25% and 50% of the α-CH content were partially replaced by a mineral admixture; and 25%, 50%, 75%, and 100% were replaced by ordinary portland cement (OPC). The hydration products and microstructural characteristics of the prepared binders were investigated using X-ray diffraction analysis and scanning electron microscopy. The portlandite [Ca(OH) 2 ] phase formed in the hydrated cementitious materials was quantified by thermogravimetric analysis to examine the relationship between Ca(OH) 2 content and pH values of the pastes. The OPC paste without α-CH showed several diffraction peaks for the Ca(OH) 2 phase, whereas the α-CH paste had no diffraction peak at the angles corresponding to Ca(OH) 2 . The dehydration mass fraction of Ca(OH) 2 corresponded to approximately 11% of the cement content included in each paste sample. The 28-day compressive strength of α-CH mortar was approximately 55% of that of OPC mortar, whereas the α-CH-based pastes without OPC maintained the pH at the neutral level, between 6.5 and 6.9, showing that the use of cement, even in very low amounts, is impractical for reducing the alkalinity of concrete. The α-CH possesses significant potential for practical production of neutral vegetation concrete.

The depletion of natural aggregates has already progressed significantly in some regions and countries, including South Korea, and it is critical to identify replacement materials to address this problem. In recent decades, researchers have focused on low-cost industrial residues or solid waste as potential solutions, and this study involves application of bottom ash (BA), a byproduct of coal-fired electrical power plants, as fine and coarse aggregates. The application of BA to the manufacture of concrete is noteworthy in terms of economic as well as ecological aspects for preserving natural resources. In the experiment, a total of 20 concrete containing bottom ash (CCBA) mixtures classified according to W/C and the bottom ash aggregate (BAA) mixing ratios were evaluated for their workability and various mechanical properties. The results of the experiment showed that the factor having the greatest effects on the mechanical properties of concrete was the usage of coarse BAA or lack thereof, and that the rates of decline in mechanical properties due to the replacement of fine BAA were within levels that could be controlled by other design factors, such as W/C. This study provides a comparison between the experimental results and the prediction results of several existing design codes, which will serve as basic data for proposing a reliable, predictive CCBA structural design model.

The effectiveness of biological coating mortars was examined by testing the variations of the compressive strength and mass of concrete and the transition of hydration products of the cement matrix in 5% sulfuric acid solutions. These biological coating mortars were originally developed in the previous investigation for enhancing the sulfate resistance of concrete. Based on the block membrane action of the glycocalyx generated from bacterial activity, Rhodobacter capsulatus was isolated and immobilized in expanded vermiculite together with a bacterial medium. Concrete cylinders were coated with a thickness of 2.5 mm using three types of mortar: conventional mortar C without bacteria and bacterial agents, mortar B with non-immobilized bacteria, and mortar I with bacteria immobilized in accordance with the proposed technique. The glycocalyx formation and the survival of bacteria in the coating mortars immersed in sulfuric acid solutions were traced by scanning electron microscopy image and the viable cell count method. Test results revealed that the proposed biological coating technique is significantly favorable for restricting the decrease in the compressive strength of concrete exposed to sulfuric acid solution, with no delamination or cracks in the concrete. Moreover, the concrete specimen I under sulfuric acid solutions exhibited very close profiles for X-ray diffraction and thermogravimetric analysis to those of virgin concrete cured under the conventional environment. There were less gypsum and ettringite from the reaction between the hydration products of cement and sulfuric acid. Overall, the proposed biological coating technique facilitates biomimetic activity, even in a strong sulfuric acid environment.

Carbonation is a typical deterioration phenomenon which accelerates steel corrosion through pH drop in pore water by intrusion of external carbon dioxide (CO2). Many researches have been performed on carbonation process considering carbonic reaction, mixture conditions, and exterior conditions. Recently probabilistic approaches have been adopted for considering engineering uncertainties such as complicated material behavior, simple evaluation system, and limited sample numbers. In the study, the service life variation was evaluated considering several effects of induced tensile stress level, cold joint, and GGBFS (Ground Granulated Blast Furnace Slag) through probabilistic approach. Utilizing the previous test results, the effect of loading conditions on carbonation depth was investigated. Four design parameters like cover depth, exterior CO2 concentration, carbonatable material, and CO2 diffusion coefficient were assumed as random variables for probability analysis. Through MCS (Monte Carlo Simulation) with normal distributions and intended PDF (Probability of Durability Failure) of 10%, variations of service life were simulated for the RC structure under loading conditions. The effects of COVs (Coefficient of Variation) for design parameters were also simulated. The comparisons of the predicted service life from the probabilistic and deterministic methods were quantitatively discussed, and the safety index with service life was also investigated. The results of this study can provide useful information on maintenance priority and service life evaluation for RC structures containing cold joint subjected to tensile stress.

As a part of the fundamental investigation to evaluate the compressive fatigue damage of fiber-reinforced lightweight concrete using high-volume supplementary cementitious materials (SCMs), the stress–strain response of the concrete was examined under cyclic loading within maximum stress levels of 0.9, 0.8, and 0.75 f c ’ and a minimum stress level fixed at 0.1 f c ’ , where f c ’ is the concrete compressive strength. To produce a high-volume SCM binder, 20% fly ash and 50% ground granulated blast-furnace slag were used as a partial replacement for cement. Amorphous steel (AS) and polyvinyl acetate (PVA) fibers were added individually or in combination considering their conventionally recommended volume fractions. The fatigue tests were carried out by controlling the load between two limits with a sinusoidal variation at a frequency of 1 Hz. Test results showed that PVA fiber was preferable to AS fiber in enhancing the fatigue life of HVS-LWC, whereas the fatigue damage of the PVA fiber concrete was lower than that of the AS fiber concrete. This trend was more notable under a higher maximum stress level. To improve the fatigue life and fatigue damage of concrete, hybridization of both fibers rather than monolithic use is recommended.

A hybrid H-steel–precast concrete (HSPC) beam system with a simple ductile connection was developed to overcome the limitations of a conventional hybrid beam system with a bolt connection between the H-steel beams supported by columns and H-steel beams embedded into the concrete beams. The developed HSPC beam system has three different sections: H-steel, joint, and reinforced concrete sections. To examine the effectiveness on the moment resistance and ductile performance of the developed HSPC beam system, five fixed-end beam specimens were tested under reversed cyclic one-point concentrated top loads at mid-span. The prepared specimens were designed as follows: H1.0, H0.5, and H0.25 were used to evaluate the effect of the location of the joint on the flexural behavior of the developed HSPC beam; P0.5 was used to introduce the prestressing force; and S0.5 was used to examine the effect of the lap splices of the headed longitudinal reinforcing bars on the stress transfer at a joint. The flexural capacity of the fixed-end HSPC beams was evaluated based on the virtual work principle under the assumption of rigid joints at the connection of the steel and concrete beams. None of the beam specimens showed shear cracks or splitting tensile cracks around the joint region until the beam failed, unlike in the conventional hybrid beam system with a bolt connection. The developed HSPC beam retained a ductility comparable to that of conventional RC beams. From the measured crack propagation, cyclic load–displacement curve, consistency of the recorded strain distribution along the beam length with the calculations, and agreement between the ultimate loads and the calculated collapse loads, the proposed joint element connecting the H-steel and RC beams can be regarded as a rigid connection, resisting the applied moments.

The purpose of the present study was to examine the high-volume use of by-products as supplementary cementitious materials (SCMs) in order to control the hydration heat of concrete and enhance its sustainability. The prepared ternary binders were composed of varying combinations of fly ash, ground granulated blast-furnace slag, and ordinary Portland cement (OPC). Isothermal hydration tests were conducted on the pastes produced using the prepared ternary binders and OPC under constant temperatures ( T ) of 13, 23, and 33 °C. Adiabatic hydration tests were also conducted on the concrete mixes at T of 23 °C. The heat production rate curve clearly showed that the induction and acceleratory periods increased with increasing SCM amount, whereas the maximum value of the curve and the decelerator period decreased; as a result, the activation energy of the cementitious pastes tended to increase with increasing SCM amount. The maximum values of total heat production determined from the adiabatic hydration tests also increased with increasing water–to–binder ratio. The relationship between the degree of reaction and the compressive strength development of the concrete was very similar in both the isothermal and the adiabatic hydration tests. The environmental impact assessment demonstrated that the very-high-volume SCM concrete had a reduction in global warming potential of 75–86% and in abiotic depletion of 73–82% as compared with OPC concrete.

RC (reinforced concrete) structures are durable and have a long service life. However, corrosion in embedded steel due to chloride ingress causes durability problems, and this poses a threat to structural performance degradation. The repair cost is very important for the maintenance of RC structures, through which the service life can be extended with reasonable performances. Unlike the conventional deterministic evaluation used to determine repair cost, the probabilistic method can provide a more reasonable result that considers various engineering uncertainties and continuous repair cost. In this paper, the repair cost for an apartment near the seashore was evaluated based on the actual concrete mix proportions and repair unit cost. Two patterns of PSLF (probabilistic service life function) using normal distribution and log distribution were considered for the repair cost evaluation. This was done after the derivation of service life was calculated based on two mix proportions. Within a given service life, various repair costs were evaluated and discussed that considered concrete mix proportions, the pattern of PSLF, and conventional techniques.

The present study developed a new and original strengthening method to enhance the shear capacity and ductility of unreinforced masonry (URM) walls based on the unbonded prestressed units using steel bars and glass fiber (GF) grids. The strengthening efficiency was validated through the experimental analyses including the failure mode, the lateral load-displacement relationship, shear capacity, and work damage indicator measured from four specimens subjected to a constant axial load and cyclic lateral loads. In addition, new design equations for the shear capacity of masonry walls were derived based on the regression analysis of 172 datasets. In particular, the proposed equations considered the shear enhancement by the axial stresses created due to the prestressed strengthening materials. The test results showed that shear capacity of the masonry walls strengthened with diagonal steel bars and GF grids increased by 4.2 times when compared with that of the companion URM walls. The proposed design equations for shear capacity of masonry walls also exhibited superior accuracy to FEMA 306 and EC 6 models.

This study aims to examine the potential of approaches proposed for transverse reinforcement arrangement in the jacket section of existing non-seismic or deficient columns to enhance the axial performance of these columns. To satisfy the requirements for the seismic details of column design specified in ACI 318-14, an original technique of arranging V-clips across the overlapped legs of channel-shape bars was proposed to form peripheral closed-hoops in the jacket section while avoiding the interruption of the existing column. Ten column specimens with large-scale dimensions were prepared by considering the jacketing method and the amount of transverse reinforcement in the jacket section as test parameters, following which they were tested under concentric axial loads by using a 40000-kN-capacity steel frame. In the test, concrete jacket columns prepared using the proposed V-clip technique showed an axial performance equivalent to that of the counterpart concrete jacket columns prepared using prefabricated bar units, the effectiveness of which was previously demonstrated in terms of the enhancement of axial stiffness, strength, and ductility as well as easier buildability for forming peripheral closed-hoops and supplementary ties in the jacket section. The restriction of the opening of the channel-shape bars by V-clips delayed the buckling of longitudinal reinforcing bars and resulted in less severe damage to the core concrete in the jacket section. Thus, concrete jacket columns reinforced with the proposed techniques exhibited higher values of axial ductility than conventional concrete jacket columns or columns jacketed with steel plates and carbon-fiber laminates.

The objective of the present study is to develop a new material through the nano-aerogel application for improving the thermal transfer and moisture resistances of preformed foam concrete. Thus, this pioneering study focused on estimating the feasibility of developing high-performance foam concrete with good thermal transfer resistance and waterproof properties by uniformly embedding a highly adiabatic and hydrophobic aerogel with nanosized pores in the porous structure of foam concrete. Methyltrimethoxysilane (MTMS), a silica-based precursor, and tetraethyl orthosilicate (TEOS) were used to manufacture the nano-aerogel material. The nano aerogels were embedded under negative pressure environments of 5–10 torr within the airtight chamber. The test results show that the nano-aerogel-embedded foam concrete possesses a thermal conductivity of approximately 0.08 W/m·K, which corresponds to be 30–50% of that measured for conventional foam concrete. The waterproof capacity of the nano-aerogel-embedded foam concrete was significantly improved, resulting in a water contact angle of 120.8° and exhibiting 75% lower water absorption at an age of 24 hours when compared with the conventional foam concrete. The integrated reactive group of the nano-aerogel materials was uniformly distributed throughout the foam concrete pores. Thus, our results suggest that nano-aerogel-embedded foam concrete has great potential as a source material for insulation in building structures.

The present study examined the effectiveness of supplementary cementitious materials (SCMs) such as ground granulated blast-furnace slag (GGBS), fly ash (FA), and silica fume (SF), in reducing CO2 emissions from ordinary Portland cement (OPC) concrete. This was done by assembling and analyzing a comprehensive database including 5294 laboratory concrete mixes and 3915 plant mixes. The database covered extensive ranges of compressive strength (8–170 MPa) and substitution levels (3–80% for GGBS, 3–70% for FA, and 3–40% for SF). The system studied for CO2 assessment of concrete based on Korean lifecycle inventory was from cradle to preconstruction, which includes consistent materials, transportation and production phases. The unit binder content and CO2 emissions of concrete in developing the unit strength (1 MPa) were identified using the binder intensity and CO2 intensity, respectively. The value of the CO2 intensity decreased sharply as the substitution level of the SCMs increased up to approximately 15–20%, beyond which the rate of decrease gradually slowed. Overall, the binder and CO2 intensities could be formulated as a function of the individual substitution level of each SCM. The proposed equations hold considerable promise as a guideline for the straightforward determination of (1) the total CO2 emission for a given concrete mix proportion, (2) the unit binder content for a targeted compressive strength, and (3) the type and substitution level of SCMs for a designed strength and targeted CO2 reduction rate.

The present study tested 16 concrete mixes to develop a high-performance aerated concrete without using high-pressure steam curing processes, as an alternative to autoclaved aerated concrete (AAC) blocks. To achieve high-strength gains, particularly at an early age, for aerated concrete under an air curing environment, the binder and chemical agent were specially contrived as follows: The loss on ignition of ordinary Portland cement was controlled to 1.5% and 3% anhydrous gypsum was then added; and the content of polyethylene glycol alkylether in a polycarboxylate-based water-reducing agent was modified to 28%. Furthermore, a foaming agent based on a protein-hydrolization with enzymatic active components was used to generate independently closed pores during concrete mixing. The test parameters investigated were the foaming volume rate ( V f ) of the preformed foam, water-to-binder ratio ( W / B ), and unit binder content ( B ). The qualities of the developed high-performance aerated concrete were compared with the minimum requirements specified in ASTM C 1693 for AAC and with data of existing conventional aerated concrete. Prediction models for dry density, compressive strength, stress–strain relationship, and thermal conductivity of aerated concrete were formulated from the regression analyses of the test data. All concrete mixes investigated displayed enhanced workability and defoaming resistance, achieving self-compactability performance. Furthermore, the measured mechanical properties prove that the developed high-performance aerated concrete has considerable potential for practical application when B is approximately 550 kg/m 3 and when W / B ranges between 30% and 25%, at which it fulfils the minimum requirement for class AAC-4 of ASTM C 1693.

To examine the size effect in direct tension, 8 ready-mixed concrete batches classified into all-lightweight concrete (ALWC) and sand-lightweight concrete (SLWC) groups were prepared. In each group, the maximum aggregate size varied between 4 mm and 19 mm, and then the lateral depth of specimen with rectangular section ranged from 100 mm to 500 mm in each concrete batch. The size effect curves based on the basic formulas proposed by Bažant (1984) [1], Kim and Eo (1990) [2], and Yang and Sim (2011) [3] were also determined using a total of 28 lightweight concrete (LWC) data of current tests and 114 normal-weight concrete (NWC) data compiled from the available literature (Carpinteri and Ferro, 1994; Hu, 2011) [4,5], though specimens with lateral depth beside 100 mm is very insufficient even in NWC. The present experimental observations and verifications by prediction models clearly showed that the size effect is more notable with the decrease of the unit weight of concrete and it is stronger in direct tension than in compression. The validity of Bažant’s model (Bažant, 1984) [1] is significantly dependent on the maximum aggregate size, while the models proposed by Kim and Eo (1990) [2] and Yang and Sim (2011) [3] closely predict the size effect trend observed from test data, confirming that the influence of the maximum aggregate size on the concrete tensile strength and the size effect is negligible, especially for LWC.

In the present study, 15 concrete mixes with dry density between 300 and 500 kg/m3 were tested for developing reliable mixing proportions, and establishing the significance of sustainable application of alkali-activated (AA) foamed concrete as a thermal insulation material in floor heating systems of buildings. Ground granulated blast-furnace slag (GGBS) was activated using the following three types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, 5% Ca(OH)2 and 6.5% Na2SiO3, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The unit binder content varied in the concrete mixes corresponding to each type of activator. All mixes were produced using the pre-formed foam procedure with no aggregate or filler. The test results revealed that AA GGBS foamed concrete has considerable potential for practical applications when the unit binder content is close to 400 kg/m3, achieving the minimum quality requirements specified in the KS F 4039 as well as ensuring economic efficiency. Furthermore, the tested AA GGBS foamed concrete developed higher compressive strength than ordinary Portland cement (OPC) foamed concrete with the same dry density. In particular, a lifecycle assessment demonstrated a reduction in the environmental impact profiles of all specimens relative to typical OPC foamed concrete as follows: 99% for photochemical oxidation potential, 85–93% for global warming potential, 73–85% for abiotic depletion, and 68–85% for both acidification potential and human toxicity. Overall, the developed AA GGBS foamed concrete can be enlarged to sustainable varieties of cast-in-place structural fill and precast masonry materials.

In this study, a straightforward mixture-proportioning procedure for structural lightweight-aggregate concrete (LWAC) was developed to determine the unit content of each ingredient to achieve the target values for slump, compressive strength, dry density, and air content of the concrete. To develop this approach, the design equations to determine the water-to-cement ratio and the unit water content were empirically formulated by performing a regression analysis over 347 data points. These data points were compiled from ordinary Portland cement concrete mixtures with expanded fly ash or clay lightweight aggregates. To determine the volumetric ratio of coarse aggregate per unit weight, a mathematical solution was established under two boundary conditions: the absolute volume and the dry density of concrete. The reliability of the proposed procedure was verified by testing five ready-mixed concrete batches at different replacement levels of lightweight fine aggregates for natural sand. In the concrete batches, expanded clay particles that were manufactured in a rotary kiln were used as the lightweight aggregates. The required values of the target parameters and the experimental values were compared. The results demonstrated that the proposed procedure provided a reasonable guide to obtain the first trial mixture of LWAC that varied with the requirements of the concrete and the properties of lightweight aggregates.

Twelve partially post-tensioned lightweight concrete (LWC) one-way slabs were tested under a symmetrical top one-point loading and a symmetrical top two-point loading. For each loading type, unbonded prestressing three-wire strands were arranged with a straight profile of constant eccentricity and a harped profile of variable eccentricity. The span-to-depth ratio also varied among 15, 35, and 55. The ultimate moment and the corresponding stress increase in unbonded tendons measured from the present LWC specimens were compared with those of post-tensioned normal-weight (NWC) concrete beams and ACI 318-11 predictions. Additionally, to generalize strain distribution-based equations to predict the stress increase in unbonded tendons at ultimate strength of flexural members, an equivalent plastic hinge length-to-tendon length ratio (to explain the reduced stress of unbonded tendons) and a coefficient (to straightforwardly obtain the neutral axis depth) were formulated from a total of 200 test data and a comprehensive parametric study, respectively. From comparisons between predictions and experimental results, the ACI 318-11 design equations for the stress increase in unbonded tendons were found to be fairly conservative in both the NWC and the LWC beams, though an unsafe condition is occasionally observed in those specimens with a reinforcing index between 0.27 and 0.35 under one-point top loading. Conversely, the predictions obtained from the currently proposed equations are in good agreement with test results.

This study examined the shrinkage behavior of heavyweight magnetite concrete up through the age of one year. The substitution level of conventional sand for magnetite fine aggregate varied from 0% to 100% in increments of 25%, and the substitution level of fly ash for cement varied from 5% up to 35%. Autogenous shrinkage strains were also measured for five different concrete mixes with fly ash and compared with predictions obtained from CEB-FIP equations. Test results showed that the shrinkage strains of heavyweight concrete (HWC) were significantly affected by the pore structure of different aggregates. Based on the experimental observations, the GL 2000 model (including time function and ultimate shrinkage strain) was modified by introducing the parameter of an equivalent porosity of aggregates to reasonably evaluate the shrinkage behavior of HWC. In general, both the CEB-FIP equations and the original GL 2000 model underestimated the shrinkage strains of HWC. This trend became more severe with the increase in ages and equivalent porosities of aggregate. In contrast, the modified GL 2000 model gave significantly more accurate results, regardless of the substitution level of conventional sand.

The present tests prepared 9 ready-mixed concrete batches to examine the influences of the concrete type and the maximum aggregate size ( d a ) on the size effect in compression. For each concrete mixing, the aspect ratios of specimens with circular or square sections were 1.0 and 2.0, while the lateral dimensions of specimens varied from 50 mm to 400 mm. A comprehensive database including the 1492 normal-weight concrete (NWC) and 363 lightweight concrete (LWC) specimens was also established in order to trace the size-effect trend in LWC through the comparisons with the modern prediction models proposed by Bažant, Neville, Kim and Eo, and Sim et al. The present study clearly showed that the size effect and the slope of the size effect became stronger with the decrease of the unit weight of concrete. The influence of d a on the size effect observed in the current NWC specimens was smaller than the predictions obtained from the models of Bažant and Kim and Eo; while it was found to be negligible for LWC. Further, the refined model of Sim et al. confirms that the gain of the compressive strength of concrete due to the increase of d a is insignificant, especially for LWC.

In this study, the size and aspect ratio effects on the compressive strength of lightweight concrete were examined using nine laboratorial concrete mixes and three ready-mixed concrete batches. At each concrete mix, the aspect ratios of specimens with circular or square sections were 1.0 and 2.0. The lateral dimension of specimens ranged between 50 and 150 mm at each laboratorial concrete mix, while it varied from 50 to 400 mm at each ready-mixed concrete batch. The present study also proposed generalized prediction models for the size effect based on the crack band theory of fracture mechanics, which can cover important influencing parameters such as the aspect ratio and lateral depth of the specimen and the unit weight of concrete. Test results showed that the crack band zone in lightweight concrete specimens was more localized with poor crack distribution than in normal-weight concrete specimens, regardless of the geometrical dimensions of the specimens. As a result, the size effect was stronger with the decrease of the concrete unit weight, and this trend was more notable in specimens with an aspect ratio of 2.0 than in those with an aspect ratio of 1.0. The compressive strength predictions of concrete obtained from the present models are in good agreement with the test results including a total of 1661 data. The trend of the size effect against different parameters as predicted by the present models has a consistent agreement with that observed from experimental results.

Although alkali-activated (AA) concrete is generally regarded as one of the most effective concrete technologies for reducing CO2 emissions, very few investigations have been carried out on the assessment of the CO2 reduction of such concrete. The present paper reports an evaluation procedure for the CO2 reduction of AA concrete. The studied system considers all of the steps from the cradle to pre-construction. CO2 reduction for secondary precast concrete products is also evaluated with reference to practical examples wherein ground granulated blast-furnace slag (GGBS) cement is replaced with AA GGBS binder. Comparisons of the performance efficiency indicators, binder and CO2 intensities, reveal that the contribution of the binder to the total CO2 emission is more significant in ordinary Portland cement (OPC)-based concrete than in AA concrete, whereas the contribution of aggregate transportation becomes more critical in AA concrete than in OPC-based concrete. The reduction rate of CO2 emission of AA concrete relative to OPC concrete commonly ranges between 55 and 75%. In addition, the CO2 reduction rate in secondary precast concrete products that use AA GGBS binder instead of GGBS cement can be evaluated as approximately 20% when the total aggregate-to-binder ratio ranges between 3.0 and 4.0. On the other hand, Ca(OH)2-based AA GGBS concrete shows a CO2 intensity that is approximately 2.4 times lower than that of OPC concrete. Overall, the slope of the increasing rate of the CO2 intensity against the binder intensity is lower in Ca(OH)2-based AA GGBS concrete than in OPC-based concrete.

The development of cementless slag-based alkali-activated mortar has previously been demonstrated. While greener than Portland cement based compositions, slag-based alkali-activated mortar tends to be highly brittle. In the present work, the feasibility of developing a new strain-hardening fiber reinforced composite using slag-based alkali-activated mortar reinforced by polyvinyl alcohol fiber is presented. In the development, three mixtures having a viscosity range that promotes uniform fiber dispersion were determined according to the types of alkali-activator and water to binder ratio. A series of experiments, including density, compression, uniaxial tension and panel bending tests were carried out to characterize the mechanical properties of the composite. Test results establish the feasibility of attaining tensile strain up to 4.7% in fiber reinforced alkali-activated slag composite, compared with 0.020% for the mortar matrix alone.

This study proposes a practical strengthening technique for enhancing the in-plane shear strength and ductility of unreinforced masonry (URM) walls using the unbonded prestressed wire rope units. Six full-scale strengthened URM walls and an unstrengthened URM wall were tested under constant axial load and cyclic lateral loads to explore the significance and limitations of the developed seismic strengthening procedure. The main variables investigated were the aspect ratio of walls, and the spacing and configuration of the prestressed wire ropes. The ductility of the walls tested was evaluated using the work damage indicator calculated at each loading step from the hysteretic loops. In addition, shear transfer capacities of masonry and wire ropes were identified based on the statistical fitting of test data for URM walls compiled from the literature and 45° truss analogy, respectively, in order to propose simple equations for shear strength of the URM walls strengthened with the developed wire rope units. Test results showed that the proposed strengthening procedure was highly effective in enhancing the in-plane shear strength and ductility of URM walls and controlling crack propagation along head and bed mortar joints. The shear strength and work damage indicator increased with the decrease of the spacing of wire ropes, showing that the inclined wire ropes were more capable of enhancing ductility than vertical wire ropes. The crack resistance capacity and stiffness of URM walls were also improved due to the additional axial compression force provided from the prestressing force applied to the wire ropes. The shear capacities obtained from the proposed simple equations were in good agreement with the test results, indicating that the mean and standard deviation of the ratios between measured and predicted shear capacities were 1.14 and 0.13, respectively.

This paper presents mechanical properties of calcium hydroxide (Ca(OH)2)-activated ground granulated blast-furnace slag (GGBS) concrete with different auxiliary activators in order to provide basic data for developing the mixing procedure and design models for structural concrete. Twelve concrete mixes were prepared with the main parameters of water–binder (W/B) ratio. The measured mechanical properties were compared, wherever possible, with design equations specified in ordinary Portland cement (OPC) concrete code provisions. The investigated Ca(OH)2-based AA GGBS concrete showed an enhanced workability, delayed slump loss and similar increasing rate of compressive strength against W/B ratio to that observed in OPC concrete. Similarly to OPC concrete, mechanical properties of Ca(OH)2-based AA GGBS concrete could be expressed as a power function of compressive strength (fc′). The values of the power in the determined equations could be approximately set to be 0.5 for modulus of elasticity, 0.65 for modulus of rupture, tensile strength and direct shear strength, and 0.75 for bond strength. Overall, the present test results revealed that the tested Ca(OH)2-based AA GGBS concrete has a considerable potential for practical application to structural concrete when the W/B ratio is lower than 30%.

To strengthen the practical application of the Ca(OH)2-based alkali-activated (AA) ground granulated blast-furnace slag (GGBS) system, the hydration products, microstructural characteristics and compressive strength development of the AA GGBS mortars were examined for 3 pastes and 21 mortar mixes according to the different auxiliary activators and curing conditions. 7.5% Ca(OH)2 was used for the main activator and either 1% Na2SiO3 or 2% Na2CO3 was added for an auxiliary activator. Test results revealed that the diffraction peaks and molar Si/Ca ratio of the calcium silicate hydrate (CSH) gels were higher for water curing than for air-dried curing and with the addition of auxiliary activators than with the use of the single Ca(OH)2. Furthermore, the addition of auxiliary activators contributed to the stabilization of CSH gels at a long-term age, showing that the molar Si/Ca ratio in CSH gels increased with the hydration time. These growth and intensity of CSH gels were consistent with higher strength development. The strength gain ratio of water-cured mortars was lower at the early ages but higher at the long-term ages than that of the companion air-cured mortars. This trend was independent of the mixing proportions of the mortars and the type of auxiliary activators. Simple equations were also proposed to predict the strength development of Ca(OH)2-based AA GGBS mortars considering the influencing parameters including the curing condition, the type of auxiliary activators and the mixing proportions. The predicted compressive strength of Ca(OH)2-based AA GGBS mortars at different ages was in good agreement with the test results, though the 3-day compressive strength was underestimated.

There are very few, if any, available experimental investigations on aggregate interlock capacity along diagonal cracks in lightweight concrete deep beams. As a result, the shear design provisions including the modification factor of ACI 318-08 and EC 2 for lightweight concrete continuous deep beams are generally developed and validated using normal weight simple deep beam specimens. This paper presents the testing of 12 continuous beams made of all-lightweight, sand-lightweight and normal weight concrete having maximum aggregate sizes of 4, 8, 13 and 19 mm. The load capacities of beams tested are compared with the predictions of strut-and-tie models recommended in ACI 318-08 and EC 2 provisions including the modification factor for lightweight concrete. The beam load capacity increased with the increase of maximum aggregate size, though the aggregate interlock contribution to the load capacity of lightweight concrete deep beams was less than that of normal weight concrete deep beams. It was also shown that the lightweight concrete modification factor in EC 2 is generally unconservative, while that in ACI 318-08 is conservative for all-lightweight concrete but turns to be unconservative for sand-lightweight concrete with a maximum aggregate size above 13 mm. The conservatism of the strut-and-tie models specified in ACI 318-08 and EC 2 decreased with the decrease of maximum aggregate size, and was less in lightweight concrete deep beams than in normal weight concrete deep beams.

A hybrid precast concrete beam system, which is a coupling of an H-steel beam and a reinforced concrete beam, was developed to propose a simple ductile connection practically useful for precast concrete structures. Three beam specimens were tested to failure to explore the effectiveness and limitations of the developed hybrid precast concrete beam system in transferring externally applied flexure to a supporting column. The three hybrid precast concrete beam specimens tested were as follows: specimen S was the control beam, and specimens U and P were used to evaluate the effect of in-situ concrete and the effect of prestressing force on the flexural behavior of the beam, respectively. Test results showed that the introduction of prestressing force for longitudinal tension reinforcement significantly improved the flexural capacity and ductility of the hybrid precast concrete beam. The flexural behavior of specimen U after placement of the upper concrete was very similar to that of the control specimen S, showing that no slippage was observed at the interface between the two concretes cast at different times. In addition, no crack was developed around the H-steel beam at the composite section region until the failure of the beams, and the strain values measured in the bottom flange of the H-steel beam were very close to the predictions calculated using elasticity theory. Furthermore, the flexural capacities predicted from extended versions of ACI 318-08 and the section laminae method were in good agreement with the test results.

Sixteen alkali-activated (AA) mortars were mixed and cured at water or air-dried conditions to explore the effectiveness and limitation for the application of barium hydroxide (Ba(OH)2) as an additional activator in calcium hydroxide (Ca(OH)2)-activated ground granulated blast-furnace slag (GGBS) system. In order to determine the optimum amount of Ba(OH)2 that is to be added, test specimens were classified into two series. For series I, the Ca(OH)2-to-GGBS ratio by weight was 0% and 7.5%, and the Ba(OH)2-to-GGBS ratio by weight varied from 0% to 10% at a spacing of 2.5% for each Ca(OH)2-to-GGBS ratio. For series II, the Ca(OH)2-to-GGBS ratio was 7.5% and 10%, and the Ba(OH)2-to-GGBS ratio varied up to 3.5%. The flow loss of fresh mortars and the compressive strength development of hardened mortars were measured. In addition, X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analyses combined with a scanning electron microscope (SEM) image were carried out to ascertain the effect of alkali activators used and the curing condition on the hydration products and the microstructural characteristics of the AA mortars. Test results clearly showed that the water curing condition was more effective than the air-dried curing condition for the formation of the denser calcium silicate hydrate (C–S–H) gels that had a higher molar Si/Ca ratio, resulting in a higher strength development. The addition of 1% Ba(OH)2 also contributed to the stabilization of C–S–H gels at long-term age, which resulted in a further increase in strength with the increase of age. At the same time, the introduction of Ba(OH)2 led to the formation of 2CaO·Al2O3·SiO2·8H2O (C2ASH8) hydrates with higher molar Si/Al and Ca/Al ratios. This would also result in a higher strength development of AA mortars tested.

A simple unbonded-type shear strengthening technique for reinforced concrete beams using wire rope units is presented. Ten two-span reinforced concrete T-beams externally strengthened with wire rope units and an unstrengthened control beam were tested to failure, to explore the significance and shortcomings of the developed unbonded-type shear strengthening technique. The main parameters investigated were the type, amount and prestressing force of wire rope units. All beams tested failed, owing to significant diagonal cracks within the interior shear span. However, beams strengthened with closed type wire rope units exhibited more ductile failure than the unstrengthened, control beam or those strengthened with U-type wire rope units. The diagonal cracking load and ultimate shear capacity of beams with closed-type were linearly increased with the increase of vertical confinement stresses in concrete owing to the prestressing force in wire rope units, while those of beams with U-type were minimally influenced. It was also observed that average stresses in closed-type wire ropes crossing diagonal cracks at ultimate strength of beams tested were much higher than those in U-type wire ropes, showing better utilization in the former case. The shear capacity of beams with closed-type wire rope units is conservatively predicted using the equations of ACI 318-05, modified to account for the external wire rope units. A mechanism analysis based on the upper bound approach of the plasticity theory is also developed to assess the load capacity of beams tested. The predictions by the mechanism analysis for beams with closed-type wire rope units are in good agreement with test results and showed a coefficient of variation slightly less than the modified ACI 318-05 equations. However, the modified ACI 318-05 equations are more conservative and simpler to use for design purposes.

This paper presents the properties of a cementless mortar developed to produce eco-friendly building material without carbon dioxide emissions and with various beneficial effects. The binder, hwangtoh binder (HB), used in this mortar was developed by reaction of a very small amount of inorganic minerals and activated hwangtoh, which is rich in silica, SiO2, and alumina, Al2O3. To investigate the compressive strength and shrinkage deformation of the cementless mortar using HB, HB mortar, water–HB ratio, fine aggregate–HB ratio, and the maximum size and grading of fine aggregate were selected as the main variables of test specimens classified into three groups. The test results presenting the effect of various parameters on the properties of HB mortar confirmed that the developed HB has a highly effective performance as a binder. The equations using nonlinear multiple regression analysis based on the test results are represented to assess the flow and 28-day compressive strength of HB mortar. Comparisons between predicted and measured flow and 28-day compressive strength show good agreement.