Denser Interfacial Transition Zone Research Articles

Bio-inspired polydopamine modification of recycled carbon fibers for improving the performance of recycled carbon fiber reinforced mortars

The hydrophobicity nature of the waste carbon fiber felt (WCF) surface results in the formation of a weak interface with the paste during the curing process of WCF concrete, which seriously affects the performance of WCF concrete and the reuse of WCF. To address this problem, this paper utilized polydopamine (PDA) for the functionalization of WCF to enhance bonding between WCF and paste. The wettability, Ca2+ complexation, and functional groups of PDA coating on WCF were analyzed by contact angle, ICP-OES, and XPS, respectively. Additionally, the effects of incorporating PDA-functionalized WCF on the flowability, compressive strength, hydration kinetics, pore structure, water absorption capillary, and SEM of mortars were tested. Experimental results showed that the PDA coating improved the wettability of WCF and enhanced the flowability of WCF mortar. What's more, the PDA coating could chelate Ca2+ and promote the formation and deposition of hydration products on the WCF surface, resulting in a denser interfacial transition zone (ITZ). Compared with ordinary WCF mortar, the compressive strength of the PDA-modified WCF mortar was increased by 18% at 28d. Furthermore, the capillary water absorption of the modified group mortar was also decreased by up to 13%, significantly enhancing the durability of mortars. This paper presents a green and simple bio-inspired method to strengthen the ITZ between WCF and paste, which is fundamentally different from the traditional modification methods, and also offers a theoretical basis and technical foundation for the sustainable utilization of WCF.

Performance-based alkali-activated seawater sea-sand concrete: Mixture optimization for mechanical, environmental, and economical objectives

This study aims to explore the viability of employing alkali-activated materials (AAMs) as alternatives for ordinary Portland cements (OPCs) in seawater sea-sand concretes, thereby promoting the sustainable utilization of marine resources in island-based constructions. Artificial seawater, sea-sand, coral coarse aggregate (CCA), normal limestone aggregate (NLA) and slag-based AAMs incorporating with 15 wt% fly ash and 5 wt% silica fume were mixed to prepare performance-based alkali-activated seawater sea-sand concrete (ASSC). The L9 (33) Taguchi orthogonal method was employed to analyze the influences of the replacement ratio of CCA for NLA, cementitious material content and water-to-binder ratio on the workability, compressive strength, splitting tensile strength, carbon dioxide equivalent (CO2-e) emission, energy consumption and cost of ASSC. Three standardized evaluation indexes and the Gray-Technique of Ordering Preferences by Similarity to Ideal Solution (TOPSIS) model were proposed to estimate the influence degree of each factor, and the suggested optimal mixture for ASSC was determined to be a replacement ratio of CCA for NLA of 50%, a cementitious material content of 440 kg/m3 and a water-to-binder ratio of 0.45. Then, the microstructure characteristics of the interfacial transition zone (ITZ) between the matrix and aggregate of ASSC for the optimal mixture were observed by scanning electron microscopy (SEM). It can be concluded that the main hydration products of ASSC had dense surface pores and internal pores of CCA, reducing the length, width and number of micro-cracks in ITZ. The substrate effect and micro-pump of CCA generate a high dense ITZ between the aggregate and matrix, which can inhibit the crack development of ASSC.

Autogenous shrinkage and hydration property of cement pastes containing rice husk ash

In this paper, the rice hush ash (RHA) with different particle size were applied to explore its effect on the autogenous shrinkage and hydration property of cement pastes. The water absorption/release behavior of RHA in cement pastes were characterized by using 1H nuclear magnetic resonance. Additionally, the microstructure and compressive strength of cement pastes containing RHA were also measured. Experimental results showed that water absorption capacity of raw RHA in cement pastes reached 0.89 g/g due to its porous structure, but reduced with the decrease of RHA particle size. The addition of RHA could mitigate the development of self-desiccation, being ascribed to the release of water from RHA after about 12 h which decreased the consumption of capillary water. The autogenous shrinkage of cement pastes containing RHA was reduced by about 41.6 %, 35.6 % and 23.8 %, respectively when the mean particle size of RHA decreased from 43.6 µm to 8.5 µm. Furthermore, the addition of RHA could shorten the dormant period and greatly enhance early-age compressive strength of cement pastes due to its water absorption effect. At later ages, the hydration degree of cement was continuously increased under the double effect of internal curing and pozzolanic reaction of RHA, resulting in the formation of the dense interfacial transition zone (ITZ) between matrix and RHA particles, ultimately improved long-term strength.

A comparative study on the properties and environmental impact of mortar with the different paste-to-aggregate ratios under direct electrical and steam curing

Direct (alternating) electrical curing (DEC) is a low-carbon rapid curing method for concrete. However, the interaction between DEC and concrete composition has not been studied. This study makes use of mortar specimens with w/c of 0.4 and various paste-to-aggregate volume ratios (P/A) to examine the effects of DEC and steam curing on the early strength rise rate, late strength development, pore structure characteristics, and environmental impact.The results show that the peak current and temperature increase with increasing P/A under constant curing voltage. The compressive strengths of specimens cured by DEC at 1 d age are greatly improved when compared with specimens cured by standard curing. It is seen that the specimen porosity under DEC is lower than steam curing, the pore diameter is refined, and a dense interfacial transition zone structure exists. It is found that DEC can reduce energy costs by nearly 2/3 compared with steam curing. And the environmental impact index of DEC is only 1/4–1/2 of that of steam curing. In summary, this paper provides am important technical support for the further establishment of DEC regimes.

A preliminary study on the efficiency of the steel slag-based spraying carbonation layer in improving the durability of cement-based products

The idea of using a steel slag-based spraying carbonation layer to improve the durability of cement-based products was proposed. The carbonation layer was prepared by spraying the steel slag-based slurry on the surface of cement-based products and then curing them with high-concentration CO2. The results showed that the carbonation layer had excellent sulfate resistance; additionally, it effectively protected the standard-cured and steam-cured mortars from sulfate attack and reduced the chloride ions migration coefficient of both standard-cured and steam-cured mortars significantly by 57.1% and 53.8%, respectively. The protection of the carbonation layer on mortars was attributed to the better pore structure of the carbonation layer and the dense interfacial transition zone of the carbonation layer and mortar matrix. The steel slag-based spraying carbonation layer recycled the steel slag, solidified CO2, and improved the durability of cement-based products, which had great environmental and engineering significance.

Enhancing the elastic modulus of concrete prepared with recycled coarse aggregates of different quality by chemical modifications

Due to the presence of attached old mortar in recycled concrete aggregate (RCA), the elastic modulus of the prepared recycled aggregate concrete (RAC) is generally lower than that of normal concrete, which limits the application of RAC as structural concrete. To improve the elastic modulus of RAC, three different chemical modification methods, including fly ash-silica fume (FS) slurry, nano-SiO2 (NS) solution and carbonation modifications, were carried out in this study. RCAs of different quality were used to verify the applicability of the three methods. The SEM and XRD tests were used to reveal the modification mechanism. The results show that the elastic modulus of RAC can be improved by any of the proposed chemical modification methods, among which the effect of the FS slurry is the most significant with the growth rate of 7.56%–10.56% in terms of different RAC. The modification effect of different methods on the elastic modulus of RAC, which is similar with the corresponding peak stress, is consistent with that on the quality of recycled aggregate. The SEM and XRD results show that the modified RAC has less micro-pores, denser interfacial transition zone and hydration products, which are also the main reasons for the improvement of the elastic modulus.

Mechanical and durability properties of C–S–H-seeded cement mortar cured at fluctuating low temperatures with granulated blast furnace slag as fine aggregates

The conservation of natural resources, efficient use of industrial side-streams, and reduction of environmental impacts are the main targets of the construction sector worldwide. However, the low ambient temperatures and long harsh winter seasons in northern regions limit the use of industrial side-streams in construction activities under cold weather conditions due to their slow strength development rate. This study aimed to develop an eco-friendly construction material suitable for construction under cold weather conditions using blast furnace slag as a binder and fine aggregate admixed with a calcium silicate hydrate seed accelerator in mortar. Natural sand (NS) was volumetrically substituted with 25%, 50%, 75%, and 100% of granulated blast furnace slag (GBFS) fine aggregate in mortar cured at fluctuating low/freezing temperatures (+5 to −5 °C), representing the late fall and early spring seasons in northern regions. The mortar's compressive strength increased with the incorporation of GBFS aggregate over the first three days of curing and decreased thereafter. A denser interfacial transition zone was captured around GBFS aggregates than NS in the three days old mortars. The deceleration influences of fluctuating low/freezing temperatures on the compressive strength development of mortars were diminished with time. Capillary water absorption increased with higher GBFS aggregate contents. Mortar with 25–50 vol.% GBFS aggregates exhibited greater frost resistance than control mortar with NS only. The incorporation of GBFS aggregate enhanced the mortar's resistance against a sulfuric acid attack. This study demonstrates the potential of GBFS aggregate for use in construction under cold weather conditions.

Influence of sustained compressive load on the carbonation of concrete containing blast furnace slag

Carbonation of concrete, in which 0%, 50% and 70% of cement was replaced by blast furnace slag (BFS), under different levels of sustained compressive load (0, 0.25, 0.5 and 0.75 times the breaking load) was investigated. The results show that the carbonation rate first decreases with load level and then above a threshold value (approximately 0.25–0.5 times the breaking load) increases with load level. The carbonation rate of BFS concrete becomes closer to that of Portland cement concrete under sustained compressive load. An investigation of the load-induced microstructure changes showed that the densification effect dominates in the carbonated zone in terms of lower porosity, denser interfacial transition zone, lower crack width and autogenous healing of fine cracks. The cracking effect plays a more significant role in the non-carbonated zone and leads to a notable increase in the carbonation rate at a high load level. The average major principle strain obtained by digital image correlation can be used to evaluate the combined effect of densification and cracking.

Micro and/or Nano-Silica modified moderate and high strength concrete: Rheology and synergistic effects on strength, elastic & inelastic behavior and microstructure

Synergistic effects of micro-silica (MS) and nano-silica (NS) on moderate and high strength concrete properties were investigated. Efficacy of micro and nano refinement remarkably increased as the W/Cm ratio decreased, and up to 37% improvement in compressive strength was obtained. Moreover, the linear-elastic region of the stress vs. strain diagrams significantly extended. As a result of the synergistic effect, a very dense interfacial transition zone was formed. The time-dependent evolution of the elastic modulus was much more effective than the compressive strength development. However, the combined use of MS and NS significantly decreased ductility.

Microstructure and shrinkage behavior of high-performance concrete containing supplementary cementitious materials

This paper investigated the influence of supplementary cementitious materials (SCM, including fly ash (FA), ground granulated blast-furnace slag (GGBS), metakaolin (MK)) on the microstructure and shrinkage behavior of high-performance concrete (HPC). The prediction accuracy of some typical shrinkage models and the correction factor kSCM were evaluated with statistical parameters RE and R2new. After analysis of shrinkage models, the kSCM*B4 model and kSCM*CEB were more suitable for the drying shrinkage and autogenous shrinkage of HPC, respectively. Although the activities of FA, GGBS, and MK were different, SCM were helpful to form a dense interfacial transition zone (ITZ) microstructure. To analyze comprehensively the effect of single or binary addition of SCM on its shrinkage properties, XRD, SEM, slump and compressive strength experiments of HPC were carried out. The diffraction peaks of Ca(OH)2 decreased with the content of FA and GGBS. The setting time of HPC was prolonged with the content of SCM. Both the decrease of FA and the increase of GGBS and MK could enhance the compressive strength of HPC. Drying shrinkage decreased with the content of FA, GGBS, and MK thanks to the refined microstructure with SCM. Autogenous shrinkage decreased remarkably with the content of FA and GGBS, however, that of MK was opposite. For the same total content of SCM, effects of binary addition of FA and MK, FA, and GGBS on the shrinkage behavior of HPC were more markedly than that of single FA. The drying shrinkage of HPC with single MK was slightly less than that with single GGBS, however, the autogenous shrinkage of HPC with single MK was significantly more than that with single GGBS.

Studies on Cent Percent Utilization of Recycled Coarse and Fine Aggregates in the Construction Industry

As a measure of conserving the resources and for creating eco-friendly environment, studies have been conducted on recycled demolished concrete aggregates (RCA) for their complete usage in the construction industry. The method adopted comprises improving the structure, physical and mechanical properties of RCA. The RCA that are obtained from impact jaw crusher, the surface of these aggregates is improved by processing it through miller machine by way of ball rotation action, where the surface defects and brittle fracture are removed without affecting the permanent mortar adhered on the aggregate, to these modified aggregates which are porous and weak in structure, the surface of the aggregates is subjected to various treatments to improve its structure. The techniques used are densification, hydrophobization, polymerization, and a combination of polymerization & densification. On these combinations, the various dosages of chemical treatments were applied and tested for their properties on coarse and fine aggregates. Finally, a combination of 2.5% of Lithium silicate treatment on coarse aggregates and 1 % colloidal silica treatment on fine aggregates has given satisfactory results in usage in concrete/cement mortar mass. On these combinations, the durability and microscopic studies (SEM, EDS, XRD) were done and it was observed that the combination has more association of silica with calcium and these resulted in more formation of C-S-H, and a dense interfacial transition zone. The aggregates applicability was tested in the field by using it for various civil works. All the tests and analyzed parameters indicate that the treated aggregates are future materials and act as a complete replacement for natural aggregates.

Study of the anti-abrasion performance and mechanism of coral reef sand concrete

In a marine environment, tidal waves carry coral reef blocks, which cause erosion and abrasion of breakwaters and other concrete structures, seriously affecting their stability and durability. In order to reveal the damage mechanism of coral reef sand concrete, herein the effects of admixtures such as fly ash, silica fume, polypropylene fiber and basalt fiber on the anti-abrasion performance and micro-hardness of coral reef sand concrete were studied. Additionally, the mechanisms of the abrasive damage and the increased performance of coral reef sand concrete were revealed by means of modern testing techniques, including X-ray diffraction and scanning electron microscope. The results revealed a linear relationship between the anti-abrasion strength and the compressive strength of the coral reef sand concrete mixed with fly ash and silica fume; whereas this correlation was not observed for the coral reef sand concrete containing fibers. Unlike ordinary aggregates, the characteristics of the coral aggregate such as the roughness, porosity, susceptibility to breakage, the irregularity of the shape, and the mineral composition were found to affect the anti-abrasion performance of the coral reef sand concrete. The roughness and the porous characteristics improved the micro-hardness of the aggregate-cement stone joints (0 μm) in the coral reef sand concrete, but there was still a weak Interfacial transition zone. Moreover, it was observed that the abrasion of the coral reef sand concrete can be reduced by the presence of a strong and dense interfacial transition zone, the crack resistance effect of the fibers, and the enhanced cohesive force of the cement mortar and fibers.

Roles of carbon nanotubes in reinforcing the interfacial transition zone and impermeability of concrete under different water-to-cement ratios

Concrete plays a central role in fundamental construction and engineering. However, the interfacial transition zone (ITZ), as the area between the aggregates and cementitious pastes, is the weakest component in concrete and always limits the properties and application of the concrete. Here, we reveal the potential of carbon nanotubes (CNTs) as superior additives for reinforcing the ITZ in concrete and the corresponding impermeability enhancement against various of water-to-cement (W/C) ratios. The results suggest that CNTs not only promote higher hydration reaction and generate more hydrated products to dense ITZ area, but also form net-like distributions to inhibit flaws propagation at the microscale. Compared with the plain concrete specimens, the addition CNTs micrified the ITZ width by 14.3–30% and reduced the abrasion crack width by 19.5–35%. The reinforcing effects of CNTs on ITZ characteristics are consistent with Gauss fitting and achieve the highest enhancement at 0.4 W/C ratio. The corresponding impermeability properties of concrete present a linear correlation with both ITZ width and abrasion crack width, which can be strengthened by approximately 10.9%-35.8% assisted by CNTs. Furthermore, selecting the appropriate W/C ratios is the key to make full use of CNTs roles in strengthening the ITZ of concrete. High W/C ratios may lead to the re-agglomeration of CNTs and low W/C ratios would promote CNTs to act as pulled-out roles and weaken their ability to inhibit flaws propagation.

Performance evaluation and microstructure characterization of seawater and coral/sea sand alkali-activated mortars

To adequately develop the application of marine resources for island construction and effectively promote the sustainability of industrial resources, this paper investigates the feasibility of using seawater and coral or sea sand as replacements for freshwater and river sand in alkali-activated mortars (AAMs) containing ground blast furnace slag (GBFS), fly ash (FA), and silica fume (SF). Five different mortar mixtures were designed: seawater and coral sand alkali-activated mortar (SC-AAM), seawater and sea sand alkali-activated mortar (SS-AAM), freshwater and river sand alkali-activated mortar (FR-AAM), seawater and coral sand cement mortar (SC-OPC), and freshwater and river sand cement mortar (FR-OPC). The differences in the workability (slump), setting time, compressive strength, flexural strength, and drying shrinkage of the prepared cement mortars and AAMs were compared. Then, the microstructure and crystalline phases of the mortar samples were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectrometry. The experimental results indicated that the utilization of seawater and coral or sea sand promoted the formation of C-S-H gel phases. Additionally, the existence of coral sand decreased the slump and initial setting time of the mortars due to the high water absorption and porosity of the coral aggregate. The SC-AAM exhibited higher compressive and flexural strengths at an early age and had a lower drying shrinkage than other AAMs, which can be attributed to the natural internal curing effect of the coral sand and the dense interfacial transition zone between the aggregate and the binders. The weak strength of coral sand had no effect on the strength development of the mortars in AAM production. However, the SS-AAM had a relatively low compressive strength and a large drying shrinkage in comparison to other mortar samples due to the existence of more free water.

Durability and microstructural properties of concrete with recycled brick as fine aggregates

To tackle the shortage of natural sand and to reduce the construction waste from clay bricks, the use of recycled bricks to replace sand as fine aggregates to produce more sustainable concrete is explored. This paper studied the effect of replacement levels of sand aggregates (SA) by recycled brick aggregates (rBA) at 0%, 50%, and 100%, and the additional water included in the mix proportion to represent the different moisture states of rBA (oven-dry, partial-dry, saturated-surface-dry) on the microstructure and durability of the concrete. The results show that the replacement of SA by rBA reduces the chloride migration but increases the water absorption, water sorptivity, drying shrinkage and carbonation. The water absorption, water sorptivity and carbonation can be minimized by reducing the additional water content. The microscopy results show that the pore structure of concrete deteriorate with the increase in the replacement because of the porous structure of rBA. Due to the pozzolanic reactivity of the rBA, the Ca(OH)2 crystals in concrete were consumed to generate hydration products, resulting in denser interfacial transition zone and enhanced adhesion between the rBA and the cement matrix.

Study of optimizing graphene oxide dispersion and properties of the resulting cement mortars

The effects of both the alkaline environment and calcium ions present in cementitious materials leads to the re-agglomeration of previously dispersed GO, and as a result decreases the dispersion of GO in cement matrix. To solve the aforementioned issues, this study compared 6 different kinds of superplasticizers (SP) to optimize the dispersion of GO in saturated Ca(OH)2 solution which can simulate the strong alkaline environment in the microstructure of cement matrix. And the mechanical properties and microstructures of the resulting cement mortar were investigated systematically. The experimental results present that, among the 6 SPs, Sika-PCE exhibits the best dispersibility with the optimal parameters found to be 30% ultrasonication energy and a SP-to-GO ratio of 1:1. Additionally, the dispersing process was found to have a significant impact on the dispersion of GO. The mechanical properties tests indicate that GO can remarkably improve the flexural and compressive strength of cement mortar in early age. The maximum improvement after 3d curing time was 15.48% for flexural strength with the addition of 0.02 wt% and 14.39% for compressive strength with the addition of 0.04 wt%. Scanning electron microscopy (SEM) and Back scattering images reveal that the incorporation of GO in the cement mortar leads to a denser matrix and stronger interfacial transition zone (ITZ) as compared to plain cement mortar. It can be also found that low GO dosage (0.02 wt%) contributes more to the hydration degree enhancement of the matrix of the cement mortar sample, while higher GO dosage (0.04 wt%) results in a denser ITZ in the cement mortar system. With the GO dosage increasing, energy dispersive X-Ray spectrum (EDS) results demonstrate a strong increasing trend in the Ca/Si ratio in both the interface and matrix regions.

Waste Valorisation using biochar for cement replacement and internal curing in ultra-high performance concrete

Abstract The degree of hydration in ultra-high performance concrete (UHPC) is known to be low due to low water-cement ratio, leading to a substantial portion of cement merely being an expensive filler. The study presented herein demonstrates the potential of biochar as a mineral additive for cement replacement in UHPC, enhancing hydration due to its internal curing and nucleation effects. Biochar was prepared by pyrolysis of locally available mixed wood saw dust and segregated into three size ranges: coarse (C): 250–500 μm, medium (M): 125–250 μm, and fine (F): smaller than 125 μm. These were then used to replace cement at 2, 5 and 8% by weight in pre-soaked condition. The rate and total heat of hydration measured by isothermal calorimetry were consistently higher for biochar samples, with coarse biochar samples generating up to 30% more heat at 96-h mark compared to the control mix. The degree of hydration, estimated from thermo-gravimetric analysis using Bhatty's method, was found to increase from 42% (in control mix) to 59% (in samples with 5% by wt. fine biochar). Fine biochar at 5% replacement also showed comparable 28-days compressive strength (144 MPa) as the control mix (150 MPa). Microstructure of hydrated pastes studied through scanning electron microscopy showed deposition of cement hydrates on the surface and inside the surface pores of biochar, with dense interfacial transition zone, further suggesting the efficacy of biochar in improving hydration.

An experimental investigation on the integral waterproofing capacity of polypropylene fiber concrete with fly ash and slag powder

The influence of polypropylene fiber (PF) on the waterproofing performance and chloride resistance of high performance concrete (HPC) made with fly ash and slag powder is comprehensively investigated from macro and micro perspectives via a series of experimental tests, including (i) slump and mechanical tests to measure the workability, (ii) capillary water adsorption tests to investigate the waterproofing capacity, (iii) chloride penetration tests to investigate the chloride resistance and (iv) mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) tests to observe the pore size distribution and the microstructure. Test results reveal that the addition of PF to HPC improves its waterproofing capacity and chloride resistance while having little effect on the workability. The waterproofing capacity and chloride resistance improve as the volume fraction of PF increases in the range of 0–1.35 kg/m3. Based on the results of MIP and SEM tests, the mechanism of the effects of PF on waterproofing and chloride resistance is also analyzed. Adding PF to the concrete mixture results in a decrease of the pore size, a decrease of the porosity, an enhancement of bonding between C-S-H and Ca(OH)2, and a much denser interfacial transition zone. All these microstructure changes contribute to the increase of the waterproofing performance and chloride resistance of PF-reinforced HPC made with fly ash and slag powder.

Physical and chemical effects of siliceous particles at nano, micro, and macro scales on properties of self-consolidating mortar overlays

The aim of this experimental investigation is to study the effect of siliceous particle at nano (0, 1, and 2% of pyrogenic nanosilica), micro (silica fume with 0, 5, and 10% cement weight replacement), and macro scales (sand with SiO2 percentages of 0, 50 and 100%) on mechanical properties, durability, and surface characteristics of self-consolidating mortars as an overlay. For this purpose, 27 self-consolidating mortar overlays (SCMOs) with a water to cement ratio of 0.4 and different mixture proportions were prepared. Mini-slump flow and V-funnel time values were determined experimentally in fresh SCMOs. Moreover, the compressive and flexural strength of mechanical strength, water absorption, porosity, abrasion resistance (as a durability property), skid resistance (as a surface characteristic), and early age shrinkage were measured. The interfacial transition zone and the microstructures were studied using scanning electron microscope (SEM), thermogravimetric analysis (TGA), and atomic force microscope (AFM). Based on the results, the synergic effect of silica based particles in nanoscale and microscale improved mechanical, durability, and frictional properties. SEM images showed that samples containing limestone sand had denser interfacial transition zone (ITZ) than siliceous sand samples due to better interlocking. Using the AFM images, high-silica sand mortar samples exhibit lower skid resistance compared to limestone type sand. Besides, incorporating siliceous sand improves the abrasion resistance (as a durability factor of the slip resistance) about 45.8% compared to lime-based samples. In addition, improvement in wear resistance caused by mineral additions is reduced by increasing the SiO2 percentage in the sand. The relation among porosity, compressive strength, and abrasion resistance was stronger in limestone type mixtures.

Properties of mortar with waste clay bricks as fine aggregate

In order to solve the problem existing in the utilization of fine recycled aggregates from crushed bricks (RCBA), the replacement of natural fine aggregate (NA) by RCBA to produce a new green recycled mortar is an important technology to develop renewable resource products and realize waste resources recycling. In this paper, in order to deeply understand the mechanism of RCBA, macroscopic and microscopic tests are carried out to study the influence of RCBA with different replacement ratios, particle sizes and additional water contents on the flowability, compressive strength and flexural strength of mortar. And the physical properties, chemical composition, mineral composition and microscopic morphology of RCBA are analyzed. The results show that the porous structure of the waste clay bricks together with the secondary mechanical crushing treatment result in the decline of the physical properties of RCBA. The fully additional water content in RCBA is beneficial to improve the flowability of mortar, but the partially additional water content in RCBA has an adverse impact. In addition, the RCBA with partially additional water content and particle size of 0–5 mm is beneficial to the improvement of mortar strength. However, the RCBA with fully additional water content and particle size of 0.15–5 mm is detrimental to the development of mortar strength. The microscopic test indicates the rough surface and pozzolanic activity of RCBA produce relatively stable and dense interfacial transition zone between the RCBA and cement paste.