The Frost-resisting Durability of High Strength Self-Compacting Pervious Concrete in Deicing Salt Environment

A high strength self-compacting pervious concrete(SCPC) with top-bottom interconnected pores was prepared in this paper. The frost-resisting durability of such SCPC in different deicing salt concentrations(0%, 3%, 5%, 10%, and 20%) was investigated. The mass-loss rate, relative dynamic modulus of elasticity, compressive strength, flexural strength and hydraulic conductivity of SCPC after 300 freeze-thaw cycles were measured to evaluate the frost-resisting durability. In addition, the microstructures of SCPC near the top-bottom interconnected pores after 300 freeze-thaw cycles were observed by SEM. The results show that the high strength SCPC possesses much better frost-resisting durability than traditional pervious concrete(TPC) after 300 freeze-thaw cycles, which can be used in heavy loading roads. The most serious freeze-thaw damage emerges in the SCPC immersed in the 3% of Na Cl solution, while there is no obvious damage in 20% of Na Cl solution. Furthermore, it can be deduced that the high strength SCPC can be used for 100 years in a cold environment.

Seismic performance of steel reinforced ultra high-strength concrete composite frame joints

To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.

STUDY ON OPTIMIZATION OF HIGH PERFORMANCE CONCRETE ADMIXTURES

Influences of admixtures on the workability and strength of high performance concrete （HPC） are in- vestigated. The types of investigated admixtures include naphthalene series high range water reducing agent, polycarboxlic series high range water reduce agent and sodium sulfate hardening accelerating agent. Two kinds of curing condition, namely steam curing condition and standard curing condition, are adopted. The result shows that HPC, added with polycarboxlic series of high performance water reducer, has high workability and strength, while sodium sulfate accelerating agent causes poor workability and low strength. Thus for vapor-cured HPC and its formulations, naphthalene series high range water reducing agent with less sodium sulfate should be given pri- ority. Therefore, the differences of curing conditions should be considered when selecting HPC admixtures.

FAILURE MODE AND CONSTITUTIVE MODEL OF PLAIN HIGH-STRENGTH HIGH-PERFORMANCE CONCRETE UNDER BIAXIAL COMPRESSION AFTER EXPOSURE TO HIGH TEMPERATURES

An orthotropic constitutive relationship with temperature parameters for plain highstrength high-performance concrete （HSHPC） under biaxial compression is developed. It is based on the experiments performed for characterizing the strength and deformation behavior at two strength levels of HSHPC at 7 different stress ratios including a=σs ： σ3=0.00：-1,-0.20：-1,-0.30 ： -1,-0.40：-1,-0.50：-1,-0.75：-1,-1.00：-1, after the exposure to normal and high temperatures of 20, 200, 300, 400, 500 and 600℃, and using a large static-dynamic true triaxial machine. The biaxial tests were performed on 100 mm×100 mm×100 mm cubic specimens, and friction-reducing pads were used consisting of three layers of plastic membrane with glycerine in-between for the compressive loading plane. Based on the experimental results, failure modes of HSHPC specimens were described. The principal static compressive strengths, strains at the peak stress and stress-strain curves were measured; and the influence of the temperature and stress ratios on them was also analyzed. The experimental results showed that the uniaxial compressive strength of plain HSHPC after exposure to high temperatures does not decrease dramatically with the increase of temperature. The ratio of the biaxial to its uniaxial compressive strength depends on the stress ratios and brittleness-stiffness of HSHPC after exposure to different temperature levels. Comparison of the stress-strain results obtained from the theoretical model and the experimental data indicates good agreement.

Evaluation of the Shear Strength of Perfobond Rib Connectors in Ultra High Performance Concrete

Since the previous strength prediction models for the perfobond rib connector were proposed based upon the results of push-out tests conducted on concretes with compressive strength below 50 MPa, push-out test is performed on perfobond shear connectors applying ultra high performance concretes with compressive strength higher than 80 MPa to evaluate their shear resistance. The test variables are chosen to be the diameter and number of dowel holes and, the change in the shear strength of the perfobond rib connector is examined with respect to the strength of two types of UHPC: steel fiber-reinforced concrete with compressive strength of 180 MPa and concrete without steel fiber with compressive strength of 80 MPa. The test results reveal that higher concrete strength and larger number of holes increased the shear strength, and that higher increase rate in the shear strength was achieved by the dowel action. The comparison with the predictions obtained by the previous models shows that the experimental results are close to the values given by the model proposed by Oguejiofor and Hosain [1].

Seismic Performance of High-Strength Short Concrete Column with High-Strength Stirrups Constraints

The seismic performance of four short concrete columns was investigated under low cycle and repeated loads, including the failure characteristics, hysteretic behavior, rigidity degeneracy and steel-bar stress. The influences of reinforcement strength, stirrup ratio and shear span ratio were also compared. Test results reveal that the restriction effect of stirrups can improve the peak stress, so the bearing capacity of specimen can be improved; for the high-strength short concrete column with high-strength stirrups, it was more reasonable to use ultimate displacement angle to reflect the ductility of the specimen, and the yield strength of high-strength stirrups should be devalued when calculating the stirrup characteristic value; the seismic performance of short column would be improved with the increase of volume–stirrup ratio and shear span ratio; the high-strength stirrups and high-strength longitudinal reinforcements did not yield when the load acting on the specimen reached the peak value, which brought adequate safety stock to these short columns. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Performances of the High Strength Low Heat Pump Concrete (HLPC)

The effects of mineral admixtures on fluidity,mechanical and hydrational exothermic behavior were studied.The results show that,double adding ways,i e,fly ash and slag were added at the same time,not only improves the fluidity of fresh concrete with low W/B and compensates the lower early compressive strength of harden concrete caused by high adding amount of fly ash, but also greatly reduces the highest temperature rise, exothermic rate and total heat liberation of 3 day of binder pastes in HLPC, and postponed the arrival time of the highest temperature rise. HLPC was prepared and applied to project practice successfully.

A Study on the Bond Strength between High Performance Concrete and Reinforcing Bar

As a preliminary study for the erection of floating structures using high performance concrete, this paper examines the bond characteristics between concrete and the reinforcing bar. Since the floating structure is constructed in aquatic environment, corrosion of the reinforcing steel is likely to develop more prematurely than in onshore structure in case of concrete cracking. A solution to this corrosion problem could use FRP rebar instead of steel reinforcement. To that goal, an experimental study is conducted on the concrete-FRP bond strength to verify if such FRP rebar develops performance comparable to the conventional steel rebar. A series of tests are performed considering the bond length of ordinary steel rebar and G-FRP rebar as test variable with respect to the strength of concrete, and the results are presented.

Strength Regularity and Failure Criterion of High-Strength High-Performance Concrete under Multiaxial Compression

Multiaxial compression tests were performed on 100 mm×100 mm×100 mm high-strength high-performance concrete （HSI-IPC） cubes and normal strength concrete （NSC） cubes. The failure modes of specimens were presented, the static compressive strengths in principal directions were measured, the influence of the stress ratios was analyzed. The experimental results show that the ultimate strengths for HSHPC and NSC under multiaxial compression are greater than the uniaxial compressive strengths at all stress ratios, and the multiaxial strength is dependent on the brittleness and stiffness of concrete, the stress state and the stress ratios. In addition, the Kupfer-Gersfle and Ottosen＇s failure criteria for plain HSHPC and NSC under multiaxial compressive loading were modified.

Properties of Sustainable High Strength Concrete with Waste Copper Slag

The present work investigates copper slag as a substitute for river sand in high-strength concrete.The concrete mixtures were manufactured with 10%,30%,50%,70%,and 100%of copper slag to evaluate the mechanical and durability properties.The experimental results indicate that replacing copper slag above 50%affects the performance characteristics of the concrete due to its high angularity and lower water absorption characteristics.The strength of concrete with 50%copper slag is improved by 5.6%,whereas the strength of concrete with 100%copper slag is reduced by 2.75%at 28 days.However,increased curing to 90days improves the strength of the former by 7.16%and reduces the latter by only 0.23%.The water absorption,porosity,and rapid chloride penetration of the concrete mixtures with 100%copper slag are increased by 10.44%,13.20%,and 19.56%compared to control concrete.Micro-structural investigations through SEM infer higher replacement of copper results in higher void formation due to its reduced water absorption.

Seismic Performance of Steel Reinforced Ultra High-strength Concrete Columns

The seismic performance of steel reinforced ultra-high-strength concrete columns(SRSHC) with various shear-span ratios(λ) were studied through a series of experiments.The concrete compressive cube strength value of experimental specimens ranged from 92.9 MPa to 108.1 MPa.The main experimental variables affecting seismic performance of specimens were axial load ratio and stirrup reinforcement ratio.The columns(λ=2.75) subjected to low cyclic reversed lateral loads failed mainly in the flexural-shear mode failure and columns(λ≤2.0) subjected to low cyclic reversed lateral loads failed mainly in the shear mode failure.Shear force-displacement hysteretic curves and skeleton curves were drawn.Coefficient of the specimen displacement ductility was calculated.Experimental results indicate that ductility decreases with axial pressure ratio increasing,and increases with stirrup reinforcement ratio increasing.Limit values of axial pressure ratio and minimum stirrup reinforcement ratio of columns are proposed to satisfy definite ductility requirement.The suggested values provide a reference for engineering application and for the amendment of the current Chinese design code of steel reinforced concrete composite structures.

INFLUENCE OF AIRCRAFT DEICER ON FREEZE-THAW DURABILITY OF HIGH PERFORMANCE CONCRETE

The influence of glycol,the main composition of the most frequently used aircraft dicer,on the freeze-thaw durability of high performance concrete（HPC）is investigated.Freeze-thaw durability of HPC is tested by accelerated freeze-thaw test.Four kinds of the solution,i.e.,tap water,3.5% NaCl solution,glycol solutions,and a LBR-A type commercial aircraft deicer are employed.Results show that freeze-thaw durability of HPC exposed to glycol solutions is closely related to the solution concentrations.The failure of HPC exposed to 3.5% glycol solution is similar to that of those exposed to 3.5% NaCl solution,i.e.,serious surface scaling.While the damage of HPC exposed to 12.5%—25% glycol solutions is postponed.Compared with glycol solution,the commercial aircraft deicer has much more negative effects on HPC freeze-thaw durability compared with 3.5% NaCl solution.In the presence of commercial aircraft deicer for HPC subjected to freeze-thaw cycles,the deterioration is mainly due to scaling and spalling.

Combined effect of steel fibres and steel rebars on impact resistance of high performance concrete

The impact properties of normal concrete (NC) and reinforced concrete (RC) specimens,steel fibre reinforced concrete (SFRC) specimens and RC+SFRC specimens with different steel fibre dosages were investigated with the drop-weight impact test recommended by ACI Committee 544.The results indicate that the number of blows to final failure is greatly increased by addition of steel fibres.Moreover,the combination of steel fibres and steel rebars demonstrates a significant positive composite effect on the impact resistance,which results in the improvement in impact toughness of concrete specimens.In the view of variation of impact test results,the two-parameter Weibull distribution was adopted to analyze the experimental data.It is proved that the probabilistic distributions of the blows to first crack and to final failure of six types of samples approximately follow two-parameter Weibull distribution.

Effect of SAP on Properties of High Performance Concrete under Marine Wetting and Drying Cycles

The internal curing effect of superabsorbent polymer(SAP) on the properties of high performance concrete(HPC) under marine wetting and drying cycles(WD cycles) was investigated. Compressive strength, hydration and chloride migration were experimentally investigated and the results were evaluated by compasison with those under fresh water curing(FW). Water absorption and porosity were also evaluated only under WD cycles. The results showed the important influence of wetting and drying cycles on the properties of SAP modified HPC properties. Carefully designed, SAP minimized the long-term compressive strength of HPC under marine WD cycles. The hydration rate was faster in the initial curing, but became lower as compared with that cured in FW. In addition, SAP improved the long-term water absorption resistance and chloride migration resistance of HPC under marine WD cycles. The examination of the porosity showed a lower increase of the volume of capillary pores in SAP modified HPC under long term WD cycles compared with that without SAP. Therefore, internal curing by SAP could improve the durability properties of HPC under marine WD cycles.

Carbonation Resistance of Sulphoaluminate Cement-based High Performance Concrete

The influences of water/cement ratio and admixtures on carbonation resistance of sulphoaluminate cement-based high performance concrete （HPC） were investigated. The experimental results show that with the decreasing water/cement ratio, the carbonation depth of sulphoaluminate cement-based HPC is decreased remarkably, and the carbonation resistance capability is also improved with the adding admixtures. The morphologies and structure characteristics of sulphoaluminate cement hydration products before and after carbonation were analyzed using SEM and XRD. The analysis results reveal that the main hydration product of sulphoaluminate cement, that is ettringite （AFt）, decomposes after carbonation.

Pore Size Distribution of High Performance Metakaolin Concrete

The Compressive strength, porosity and pore size distribution of high performance metakaolin (MK) concrete were investigated. Concretes containing 0,5% , 10% and 20% metakaolin were prepared at a water / cementitious material ratio ( W/C) of 0. 30. In parallel, concrete mixtures with the replacement of cement by 20% fly ash or 5 and 10% silica fume were prepared for comparison. The specimens were cured in water at 27℃ for 3 to 90 days. The results show that at the early age of curing (3 days and 7 days), metakaolin replacements increase the compressive strength, but silica fume replacement slightly reduces the compressive strength. At the age of and after 28 days , the compressive strength of the concrete with metakaolin and silica fume replacement increases. A strong reduction in the total porosity and average pore diameter were observed in the concrete with MK 20% and 10% in the first 7 days.

Characterization of Surface Hardness and Microstructure of High Performance Concrete

The relationship between compressive strength obtained by universal testing machine and rebound value obtained by the hammer of high performance concrete was systematically investigated at the macro level. And a model of high performance concrete strength curve was established from them. At the micro level, the microstructure, hydration products and pore structure of concrete surface were analyzed by scanning electron microscopy（SEM）, comprehensive thermal analysis（TG-DSC） and mercury intrusion porosimetry（MIP）, respectively. The effect of carbonation on surface strength was also investigated. The results showed that the concrete surface hardness layer grew rapidly at early stage and then stabilized at last with ongoing curing age; the rebound value and compressive strength of concrete with slag were higher than those of concrete with the same content of fly ash. In addition, the strength curve obtained by the least square method can satisfy the local standard requirements with an average relative error of 8.9% and a relative standard deviation of 11.3%. When the carbonation depth was 6 mm, the compressive strength calculated by national uniform strength curve was 25 PMa higher than that by high performance concrete.

High Performance Concrete and Its Typical Mixes

With the modern development of chemical and mineral admixtures, it is now possible to produce much higher performance concrete than before. Higher performance does not only mean higher strength, but also better durability, lower risk of thermal cracking and higher dimensional stability etc. The three most effective admixtures for producing high performance concrete are superplastieizer, pulverized fuel ash and condensed silica fume. This paper outlines the properties of these materials and presents some practical guidelines for their usage.

Shrinkage Behavior of High Performance Concrete at Different Elevated Temperatures under Different Sealing Conditions

The shrinkage behavior of high performance cement concrete made from Portland cement, ultra fine granulated blast furnace slag and pulverized fly ash with addition of superplasticizer at different temperatures from ambient temperature to 120 ℃ under different seuliug conditions was investigated by means of length change measurement on cylindrical concrete specimens along with curing age. Results show that drying shrinkage deformations of titled concrete specimens increased rapidly as the curing temperature rose. The development of dryiing shrinkage deformatian can be efficiently controlled with the aid of aluminum tape sealing as compared with the unsealed specimens, especially when the curing temperature is below 60℃ , although it will increase dramatically when the curing temperature is elevated to above 90%＂ . Polymer coating on concrete specimens showed a similar effect on the control of drying shrinkage as the sealing operation with aluminum tape.

Design and Preparation of High Elastic Modulus Self-compacting Concrete for Pre-stressed Mass Concrete Structures

Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.