Repair of Second-Generation Recycled Fine Aggregate of Waste Concrete from Freeze-Thaw Environment by Carbonation Treatment

The reuse of waste recycled concrete from harsh environments has become a research hotspot in the field of construction.This study investigated the repair effect of carbonation treatment on second-generation recycled fine aggregate(SRFA)obtained from recycled fine aggregate concrete(RFAC)subjected to freeze-thaw(FT)cycles.Before and after carbonation,the properties of SRFA were evaluated.Carbonated second-generation recycled fine aggregate(CSRFA)at five substitution rates(0%,25%,50%,75%,100%)to replace SRFA was used to prepare carbonated second-generation recycled fine aggregate concrete(CSRFAC).The water absorption,porosity and mechanical properties of CSRFAC were tested,and its frost-resisting durability was evaluated.The results showed after carbonation treatment,the physical properties of SRFA was improved and met the requirements of II aggregate.The micro-hardness of the interfacial transition zone and attached mortar in CSRFA was 50.5%and 31.2%higher than that in SRFA,respectively.With the increase of CSRFA replacement rate,the water absorption and porosity of CSRFAC gradually decreased,and the mechanical properties and frost resistance of CSRFAC were gradually improved.Carbonation treatment effectively repairs the damage of SRFA caused by FT cycles and improves its application potential.

Influence of Recycling Waste Glass as Fine Aggregate on the Concrete Properties

Recent years have witnessed an increase in the quantity of waste glass(WG)across the globe.Replacing the fine aggregate with WG is one of the steps toward preserving the natural resources of the environment and creating low-cost concrete.The present study is concerned with replacing fine aggregates with glass powder(GP)at(0%,15%,30%,and 50%).It has studied the fresh and hardened properties(compressive strength,tensile strength,hardened density,and slump)for all the mentioned percent replacements.The findings have shown that all mixtures containing GP gave acceptable slump results within the design limits(2–5 cm)according to ACI standard 211.1.It has been observed that increasing the proportion of GP led to a decrease in the weight of concrete.Lastly,replacing GP with sand by 30%has led to an increase in the compressive strength by about 2.4%and 12.45%,and the tensile strength by about 2.5%and 26.54%at 7-and 28-d,respectively in comparison to normal concrete.

Mechanical Behavior Based on Aggregates Microstructure of Ultra-high Performance Concrete

We developed ultra-high performance concrete(UHPC)incorporating mullite sand and brown corundum sand(BCS),and the quartz sand UHPC was utilized to prepare for comparison.The properties of compressive strength,elastic modulus,ultrasonic pulse velocity,flexural strength,and toughness were investigated.Scanning electron microscopy and nanoindentation were also conducted to reveal the underlying mechanisms affecting macroscopic performance.Due to the superior interface bonding properties between mullite sand and matrix,the compressive strength and flexural toughness of UHPC have been significantly improved.Mullite sand and BCS aggregates have higher stiffness than quartz sand,contributing to the excellent elastic modulus exhibited by UHPC.The stiffness and volume of aggregates have a more significant impact on the elastic modulus of UHPC than interface performance,and the latter contributes more to the strength of UHPC.This study will provide a reference for developing UHPC with superior elastic modulus for structural engineering.

Methods for Improving Volume Stability of Steel Slag as Fine Aggregate

Suitable methods for enhancing the volume stability of steel slag utilized as fine aggregate were determined. The effects of steam treatment at 100 ℃ and autoclave treatment under 2.0 MPa on the soundness of steel slag sand were investigated by means of powder ratio, linear expansion, compressive and flexural strength. DTA, EDX, XRD and ethylene glycol methods were employed to analyze both the treated slags and susceptible expansion grains. Experimental results indicate that powder ratio, content of free lime and rate of linear expansion can express the improvement in volume stability of different treated methods. Steam treatment process cannot ultimately prevent specimens from cracking and decrease of strength, but mortar made from autoclave treated slag keeps integration subjected to hot water of 80℃ until 28 d and its strength do not show significant decrement. The hydration of over-burn free lime and periclase phase are the main cause for the disintegration or crack of untreated and steam treated steel slag＇s specimens. Autoclave treatment process is more effective than steam treatment process on enhancement of volume stability of steel slag.

Controlled low-strength material incorporating recycled fine aggregate from urban red brick based construction waste

Sixteen controlled low-strength material( CLSM)mixtures with various cement-to-sand( C/Sa) ratios and water-to-solid( W/So) ratios were prepared using recycled fine aggregate from urban red brick based construction waste.The fluidity and bleeding of the fresh CLSM mixtures were measured via the modified test methods, and the hardened CLSM mixtures were then molded to evaluate their compressive strength and durability. The results showthat the fluidity of the fresh CLSM mixtures is 105 to 227 mm with the corresponding bleeding rate of 3. 7% to 15. 5%, which increases with the increase in fluidity. After aging for 28 d,the compressive strength of the hardened CLSM mixtures reaches 1. 15 to 13. 96 M Pa, and their strength can be further enhanced with longer curing ages. Additionally, the strength increases with the increase of the C/Sa ratio, and decreases with the increase of the W/So ratio under the same curing age. Based on the obtained compressive strength, a fitting model for accurately predicting the compressive strength of the CLSM mixtures was established, which takes into account the above two independent variables( C/Sa and W/So ratios).M oreover, the durability of the hardened CLSM mixtures is enhanced for samples with higher C/Sa ratios.

Effect of waste concrete with different strength on mechanical properties of recycled fine aggregate mortar

The influence of source concrete (SC) with different compression strengths on the workability and mechanical properties of recycled mortar made with river sand substituted by 100% fine recycled concrete aggregates (FRCA) is experimentally investigated. The basic physical performance test shows that with the increase in SC strength, FRCA exhibit lower water absorption and crushing index, meanwhile keeping higher densities. Mechanical property tests, including compressive strength, flexural strength and uniaxial compressive stress-strain tests, show that compressive strength,flexural strength and elasticity modulus of recycled sand mortars increase roughly with the increase in SC strength. The proposed mixture design method demonstrates that all of the components can be kept as the same as those in natural mortar mixture design and FRCA must be pre-wetted before making mortar mixture. Meanwhile, the reuse of higher strength SC can ensure that recycled mortar mixtures are able to achieve similar mechanical performance when compared to natural mortar designs.

Strength and Chloride Diffusion Behaviour of Three Generations of Repeated Recycled Fine Aggregate Concrete

The feasibility of using different generations of recycled fine aggregate（RFA） in structural concrete in a chloride environment was evaluated by studying the performance of the RFA and the corresponding concrete. The different generations of RFA were recycled by following the cycle of ‘concrete-waste concrete-fine aggregate-concrete＇. The properties of three generations of repeatedly recycled fine aggregate（RRFA） were systematically investigated, and we focused on the compressive strength and splitting tensile strength and chloride ion permeability of the related structural concretes with 25%, 75%, and 100% replacement of natural fine aggregates with RFA. The results indicated that the quality of RRFA presents a trend of slow deterioration, but the overall performance of all RRFA still fulfils the quality requirements of recycled fine aggregate for structural concrete. All RRFA concretes achieved the target compressive strength of 40 MPa after 28 days except for the second generation of the recycled aggregate concrete and the third generation of the recycled aggregate concrete with 100% replacement, and all the concrete mixes achieved the target compressive strength after 90 days. The insights obtained in this study demonstrate the feasibility of using at least three generations of RRFA for the production of normal structural concrete with a design service life of 100 years in a chloride environment.

Mathematical models for properties of mortars with admixtures and recycled fine aggregates from demolished concretes

In order to expand the engineering application of recycle aggregate mortars （RAM） with aggregates from demolished concretes, the models for the properties of RAM and the replacement rate of these recycled fine aggregates were proposed. First, different kinds of mathematical models for the basic properties （compressive strength, water retention rate, and consistency loss） of RAM with two kinds of admixtures, thickening powders （TP） and self-made powdery admixtures （SSCT） designed for RAM, and the replacement rates were established, while the average relative errors and relative standard errors of these models were calculated. Additionally, the models and their error analyses for the curves of drying shrinkage and curing time of RAM ＋ SSCT at different replacement rates were put forward. The results show that polynomial functions should be used to calculate the basic properties of RAM ＋ TP and RAM ＋ SSCT at different replacement rates. In addition, polynonfial functions are the most optimal models for the sharp shrinkage sections in the curves of drying shrinkage-curing time of RAM ＋ SSCT, while exponential functions should be used as the models for the slow shrinkage sections and steady shrinkage sections.

Fractal Dimension Analysis of the Fine Aggregate Gradation of Interlocking Skeleton Asphalt Mixture

By analyzing the fine aggregate gradation scales from standards,fine aggregate in the asphalt mixture is regarded as a whole research object and fractal dimensions X of the samples were obtained by linear regression and（AC-13）is 2.43-2.56,Sup-13 is 2.28-2.54,SMA-13 is 2.66-2.88 and SAC-13 is 2.54-2.73.In the dense gradation mixture,there are little different between fractal dimensions of coarse and fine aggregates but it makes sense for skeleton asphalt mixture.For a given coarse aggregate gradation and the same percentage of coarse aggregates,the compressive strengths and splitting strengths of the asphalt mixture are studied when the fractal dimensions are selected as 2.60,2.65 and 2.70,respectively.When asphalt-stone ratio is less than optimal asphalt-stone ratio,the higher compressive strength is,the bigger X can be gotten.When asphalt-stone ratio is larger than optimal asphalt-stone ratio,little difference of compressive strength can be observed under these three conditions.The largest splitting strength can be got when X is 2.65,and larger splitting strength can be observed with the ascending of the asphalt-stone ratio.

Properties of Cementitious Rendering Mortar Prepared with Recycled Fine Aggregates

The results of an experimental study on investigating the properties of cementitious rendering mortars prepared with a recycled fine aggregate（RA） were presented.The RA was obtained from a recycling plant in which mixed demolition wastes were processed by mechanical crushing,sieving and sorting operations.Two series of rendering mortar mixes were prepared with a constant water/cement and a constant aggregate/cement ratios of 0.55 and 3 respectively.River sand and natural crushed rock fine were originally used in the two series separately,and they were consistently replaced by 25%,50%,75% and 100% by the recycled aggregate.The experimental results showed that mechanical properties,such as compressive strength,flexural strength and modulus of elasticity of the mortars prepared with the RA were lower than the mortars made with the natural aggregates.Nevertheless,the bond strength at the interface between the mortar and masonry bricks determined by the Triplet test was found to be higher for the mortars prepared with the RA.

Relation between Modulus of Elasticity and Compressive Strength of Ultrahigh-Strength Mortar with Mixed Silicon Carbide as Fine Aggregate

Ultrahigh-strength mortar mixed surface-oxidized silicon carbide as a fine aggregate was prepared by means of press-casting followed by curing in an autoclave. The relation between modulus of elssticity up to 111 GPa and compressive strength up to 360 MPa of mortar mixed silicon carbide was discussed and it was revealed that the contributions of the aggregate hardness and of the interfacial strength between the aggregate and the cement paste on the elasticity of mortar were imporant.

Rheology of Cement Mortars with Crushed Fine Aggregates of Different Lithological Types

Crushed fine aggregates are widely used for full or partial replacement of natural sands in concretes. The crushed sands present different characteristics from the natural sand, especially if taking into account the content of microfine particle, the distribution of particle sizes, the shape features, besides the different lithological origin. From the rheological point of view, the crushed sands frequently provide mixtures with high yield stress, high viscosity, high cohesion and internal friction, which hinders its use in concrete. This study is focused on the evaluation of the rheological behavior of concrete mortar phase when using different lithological types of crushed sand in total replacement of natural sand. The lithological types surveyed were granite, calcitic limestone, dolomite limestone and mica schist. Each of these sand types was studied in two ways： in natura and with adjusted grading curve. The results show the best performance of calcitic limestone providing lower viscosities and lower yield stress in mortars.

Analysis of Harnessing Waste Fine Aggregate for Sustainable Production of Concrete Elements

This paper focuses on cement composites based on waste fine aggregate obtained from hydroclassification all-in-aggregate in the Central Pomerania region in northern Poland. In the world there are regions with poor supplies of coarse aggregate, which is one of the most essential raw materials used for production of ordinary concrete. In these regions, instead of coarse aggregate, there are often very large deposits of fine aggregate such as natural sand and fine all-in-aggregate. These raw materials may be used for concrete production of standard mechanical properties. Manufacturing concrete based on locally available fine aggregate is inexpensive which encourages the local production of fine aggregate cement composites instead of ordinary concrete, requiring gravel transported from distant places.

Assessment of Bholari River Sand for Its Geotechnical Characterization as Fine Aggregate

Present study is aimed at assessment of Bholari river sand for its geo­technical characterization and suitability as fine aggregate which is being quarried in Jamshoro district,Sindh,Pakistan.For this purpose,sand samples(n=11)were collected from quarry sites and main river channel.Physical properties reveal that Bholari sand is mainly coarse to fine in size(0.2 mm-5 mm).Average values of fineness modulus,specific gravity,bulk density and void content of collected samples are 2.58,2.56,1659.90 kg/m^(3) and 35.12%respectively which varied within the corresponding permissible ranges of ACI(American Concrete Institute).Carbonate content of about 57.59%is also in agreement with corresponding range for fine aggregate.Petrographic examination revealed that Bholari River sand mainly compris­es of quartz and rock fragments with subordinate limestone fragments.As per classification of Dott(1964),Bholari sand is lithic arenite where quartz(50%)occurs as main mineral followed by rock fragments(30%),feldspars(15%)and other opaque minerals(5%).Texturally,the sediments are angu­lar(77%)to sub-round(33%).All these physical properties lie within the range set by National Highway Authority(NHA)and American Standard of Testing Material(ASTM).It is concluded that Bholari River sand is suita­ble for use in concrete mixed with cement and asphalt.

Effects of admixture on properties of recycled aggregate mortar

Compared with strengthening the recycled fine aggregate(RFA)from construction and demolition waste,which is time-consuming and complex,adding admixture into the mixtures directly is more efficient and effective to expand the application of recycled aggregate mortar(RAM).The admixture(named as SSC),mixed with sodium hexametaphosphate,sodium ligninsulfonate and citric acid,was directly added into the RAM.First,the compositions and physical properties of the RFA and reference aggregate were studied,respectively.The properties of fresh and hardened mortars were then investigated.The results show that there is a clear difference between the RFA and reference aggregate,and the properties of RAM without SSC are not as good as those of normal mortar.However,the consistency value,water retention rate,compressive strength and setting time values of RAM increase by 5%,7%,66%and 67%,and its consistency loss and density values decrease by 42%and 4%after the SSC is added into the RAM.Therefore,improving the properties of RAM through adding admixture is an effective and efficient approach to expanding its application.

Fresh and hardened properties of high-strength concrete incorporating byproduct fine crushed aggregate as partial replacement of natural sand

This paper presents the fresh and hardened properties of high-strength concrete comprising byproduct fine crushed aggregates(FCAs)sourced from the crushing of three different types of rocks,namely granophyre,basalt,and granite.The lowest void contents of the combined fine aggregates were observed when 40%to 60%of natural sand is replaced by the FCAs.By the replacement of 40%FCAs,the slump and bleeding of concrete with a water-to-cement ratio of 0.45 decreased by approximately 15%and 50%,respectively,owing to the relatively high fines content of the FCAs.The 28 d compressive strength of concrete was 50 MPa when 40%FCAs were used.The slight decrease in tensile strength from the FCAs is attributed to the flakiness of the particles.The correlations between the splitting tensile and compressive strengths of normal concrete provided in the AS 3600 and ACI 318 design standards are applicable for concrete using the FCAs as partial replacement of sand.The maximum 56 d drying shrinkage is 520 microstrains,which is significantly less than the recommended limit of 1000 microstrains by AS 3600 for concrete.Therefore,the use of these byproduct FCAs can be considered as a sustainable alternative option for the production of high-strength green concrete.

Recycled glass replacement as fine aggregate in self-compacting concrete

With increasing environmental pressure to reduce solid waste and to recycle as much as possible,the concrete industry has adopted a number of methods to achieve this goal by replacement of waste glass with concrete composition materials.Due to differences in mixture design,placement and consolidation techniques,the strength and durability of Self Compacting Concrete(SCC)may be different than those of conventional concrete.Therefore,replacement of waste glass with fine aggregate in SCC should deeply be investigated compared to conventional concretes.The aim of the present study is to investigate the effect of glass replacement with fine aggregate on the SCC properties.In present study,fine aggregate has been replaced with waste glass in six different weight ratios ranging from 0%to 50%.Fresh results indicate that the flow-ability characteristics have been increased as the waste glass incorporated to paste volume.Nevertheless,compressive,flexural and splitting strengths of concrete containing waste glass have been shown to decrease when the content of waste glass is increased.The strength reduction of concrete in different glass replacement ratios is not remarkable,thus it can be produced SCC with waste glass as fine aggregate in a standard manner.

Recycling of waste glass as aggregate in cement-based materials

Glass is a common material made from natural resources such as sand.Although much of the waste glass is recycled to make new glass products,a large proportion is still being sent to landfill.Glass is a useful resource that is non-biodegradable,occupying valuable landfill space.To combat the waste glass that is heading to landfill,alternative recycling forms need to be investigated.The construction industry is one of the largest CO_(2) emitters in the world,producing up to 8% of the global CO_(2) to produce cement.The use of sand largely depletes natural resources for the creation of mortars or concretes.This review explores the possibilities of incorporating waste glass into cement-based materials.It was found waste glass is unsuitable as a raw material replacement to produce clinker and as a coarse aggregate,due to a liquid state being produced in the kiln and the smooth surface area,respectively.Promising results were found when incorporating fine particles of glass in cement-based materials due to the favourable pozzolanic reaction which benefits the mechanical properties.It was found that 20% of cement can be replaced with waste glass of 20 mm without detrimental effects on the mechanical properties.Replacements higher than 30% can cause negative impacts as insufficient amounts of CaCO_(3) remain to react with the silica from the glass,known as the dilution effect.As the fine aggregate replacement for waste glass increases over 20%,the mechanical properties decrease proportionally;however,up to 20% has similar results to traditionally mixes.