Experimental Performance Measures of Recycled Insulation Concrete Blocks from Construction and Demolition Waste

Construction and demolition(C&D)waste has seriously affected the ecological environment.The utilization of C&D waste resources can greatly alleviate this problem,and it is an important way to help achieve the goal of zero carbon in 2050.In this study,insulation concrete blocks were developed with recycled aggregates,cement,fly ash as main raw materials,expanded polystyrene(EPS)insulation boards as block insulation filling material,and selfdeveloped construction waste composite activator,interface enhancer,surface modifier and other additives.Through experimental research and performance test analysis,the best mix ratio of the product and the mechanism of each additive were proved.The experimental results showed that the insulation concrete block prepared under the conditions of recycled aggregates sand ratio of 45%,active activator Na_(2)SO_(4)content of 0.15%and fly ash content of 30%has the best performance and meets the relevant standards.

Analysis of Waste in the Production of Concrete Blocks---A Case Study in the Goias Industry

An ever more demanding consumer market and the need for companies to be more competitive have led organizations to try to eliminate waste. This research is a case study which presents a proposal for intervention in order to improve performance of a pre-cast concrete block factory in outer Goihnia. As a first step, waste in the production process was identified through analysis of data on time involved in each step of the process. Then, applying the concepts of lean production, a list of activities was drawn up with a view to eliminating non-value-added work, identifying waste, decreasing cycle time, streamlining the production process and increasing the flexibility and transparency of the process. From the results, it was possible to identify the sources of waste and provide management with information for strategic decisions about production. Finally, various suggestions were made with a view to eliminating or mitigating bottlenecks in the production process.

Quality Assessment of Concrete Blocks Exposed in Nature for Eighty Years

The concrete blocks used on a jetty in Shanghai were made in 1909 and 1910. Having been exposed in nature for 80 years, now there are 4600 pieces of blocks left on the jetty. Comprehensive inspections, such as external appearance examination, core-drilling of concrete blocks, ultrasonic detection, nuclear densimeter inspection and in-door and out-door chemical analysis, show that 75% of the blocks are of the rebound number of 21 - 23, and the saturated limit compressive strength and dry limit compressive strength of 10MPa; the carbonized depth of concrete is 1 - 2 mm. Compared with the state of the jetty in 1968, already used for 60 years then, the jetty is expected to serve another 40 years or more after being repaired.

Properties of fiber incorporated concrete blocks manufactured using recycled aggregates

The construction and demolition industry generates a significant quantity of concrete waste,presenting an environmental challenge.The concrete waste generated can be processed to produce Recycled Aggregates(RA)of various sizes.Utilization of Recycled Aggregates(RA)as a substitute to conventional aggregates in concrete has captured considerable attention in the past few years,owing to its promising environmental and economic advantages.However,the combined utilization of recycled fine and coarse aggregate in the production of concrete for low-strength application has not been adequately explored.In this article,an attempt is made to investigate the characteristics of concrete blocks made with RA and polypropylene fiber(PF)are investigated for different cement content.Cement and PF content varied from 8 to 12%and 0%to 2%respectively in production of concrete blocks using Recycled Fine Aggregates(RFA)and Recycled Coarse Aggregates(RCA)at different replacement intervals.Water absorption of blocks manufactured across all replacement intervals of RA was less than 10%.Blocks containing 75%RFA and 25%RCA resulted in improved compressive strength of the order more than 3.8 MPa.Rate of improvement in compressive strength of block was 11%to 20%and 6.5%to 8.2%when the fiber dosage was increased from 0.5%to 1%and 1%to 2%respectively.The optimal fiber dosage was found to be 1%,beyond which no notable improvement in mechanical properties of blocks was observed.Use of RA in concrete blocks reduced embodied energy by 19%to 24%for varying cement content from 8-12%.Cost of blocks was found to be reduced by 10-15%when made with PF dosage of 0 to 2%with 8%cement content.

Characteristic parameters and radon exhalation rates of aerated concrete blocks

Objective:To understand the characteristic parameters and radon exhalation rates of aerated concrete blocks.Methods:A total of 39 nationally inspected samples were measured.Their dry density was determined based on their mass and volumes,their porosities were measured on the principle of volumetric expansion,and their radium content was determined using a high-purity germanium(HPGe)detector for gamma-ray spectroscopy.Furthermore,their diffusion lengths were quantified by establishing a combined cumulative and diffusion chamber,and their radon exhalation rates were measured through closed-box testing using a continuous radon monitor.Results:The aerated concrete blocks exhibited dry densities ranging from 464 to 840 kg/m^(3)[average:(654.0±82.5)kg/m^(3)],open porosities from 67.1%to 81.1%[average:(74.3±3.3)%],radium(^(226)Ra)content from 12.3 to 136 Bq/kg[average:(63.0±30.4)Bq/kg],diffusion lengths from 0.49 to 1.01 m[average:(0.70±0.15)m],and radon exhalation rates from 0.6 to 22.8 Bq·m^(-2)·h^(-1)[average:(7.3±5.3)Bq·m^(-2)·h^(-1)].Conclusion:Aerated concrete blocks exhibit significantly higher porosities,diffusion lengths,and radon exhalation rates than traditional concrete and clay bricks.These blocks might contribute to the high indoor radon concentration observed in modern buildings in China.

Experimental study on the compressive strength of grouted concrete block masonry based on nondestructive detection methods

Existing nondestructive detection methods were adopted to test the compressive strength of grouted concrete block masonry,i.e.the rebound method,pulling-out method and core drilling method were employed to test the strength of block,mortar and grouted concrete,respectively.The suitability of these methods for the testing of strength of grouted concrete block masonry was discussed,and the comprehensive strength of block masonry was appraised by combining existing nondestructive or micro-destructive detection methods.The nondestructive detection test on 25 grouted concrete block masonry specimens was carried out.Experimental results show that these methods mentioned above are applicable for the strength detection of grouted concrete block masonry.Moreover,the formulas of compressive strength,detection methods and proposals are given as well.

Coupled Conductive-Convective-Radiative Heat Transfer in Hollow Blocks with Two Air Cells in the Vertical Direction Subjected to an Incident Solar Flux

This work presents the results of a set of steady-state numerical simulations about heat transfer in hollow blocks in the presence of coupled natural convection,conduction and radiation.Blocks with two air cells deep in the vertical direction and three identical cavities in the horizontal direction are considered(typically used for building ceilings).Moreover,their outside horizontal surface is subjected to an incident solar flux and outdoor environment temperature while the inside surface is exposed to typical indoor environment conditions.The flows are considered laminar and two-dimensional over the whole range of parameters examined.The conservation equations are solved by means of a finite difference method based on the control volumes approach,relying on the SIMPLE algorithm for what concerns the coupling of pressure and velocity.The effects of the number of cells in the horizontal direction and the thermal conductivity on the heat transfer through the alveolar structure have been investigated.The results show that the number of holes has a significant impact on the value of the overall heat flux through the considered structure.

Mechanical Behavior of Concrete Block Masonry

The main objective of this study is to verify, through compression tests on different prisms, the vertical and horizontal deformability and the failure modes of the components of concrete blocks under compression. In this study two mortar mixes were tested, along with two types of prism, with and without the presence of a vertical joint. The conclusions were： the appearance of non-linearities of the masonry corresponds to an increase in the lateral strain due to extensive cracking of the material and a progressive increase in the Poisson ratio, the cracks in the three-block prisms built with the mortar type I were vertical, occurring symmetrically on both sides; the prisms built with mortar type II had, as a consequence of localized crushing, an association with vertical cracks due to the concentrations of stresses at some points, the presence of a vertical joint led to the appearance of separation cracks between the middle block and the vertical mortar joint, when the stress reached approximately 30% of the compressive strength of the set; the prisms with two whole blocks and one vertical joint （B） built with the mortars of mixes I and II had a compressive strength of the order of 42% and 66% of the prisms with three whole blocks （A）, respectively.

Elements of Structural Masonry Reinforced with Sisal Fibers

There is great interest in the use of natural fibers as reinforcement to obtain new construction materials due to its low cost, high availability and reduced energy consumption for its production. This paper evaluates the incorporation of sisal fibers of 20 mm and 40 mm in length and volume fraction of 0.5% and 1% for concrete masonry structural blocks, and determines the use of these units to build prisms and mini-walls. Laboratory tests were carried out to characterize the physical of blocks and mortar, in addition to the axial compression tests of the units, prisms, and mini-walls. The sisal had low apparent density and high water absorption, which is a common feature of such material due to the high incidence of permeable pores. The physical properties of the blocks with and without addition complied with the standard requirements established to validate their use. The obtained results showed that the fiber-reinforced mini-walls obtained values very close to or even higher than those obtained for the mini-walls without fibers, demonstrating better performance than the blocks and prisms.

Ductility improvement of GFRP-RC beams using precast confined concrete block in compression zone

Fiber-reinforced polymers(FRPs)have received considerable research attention because of their high strength,corrosion resistance,and low weight.However,owing to the lack of ductility in this material and the quasi-brittle behavior of concrete,FRP-reinforced concrete(FRP-RC)beams,even with flexural failure,do not fail in a ductile manner.Because the limited deformation capacity of FRP-RC beams depends on the ductility of their compression zones,the present study proposes using a precast confined concrete block(PCCB)in the compression zone to improve the ductility of the beams.A control beam and four beams with different PCCBs were cast and tested under four-point bending conditions.The control beam failed due to shear,and the PCCBs exhibited different confinements and perforations.The goal was to find an appropriate PCCB for use in the compression zone of the beams,which not only improved the ductility but also changed the failure mode of the beams from shear to flexural.Among the employed blocks,a ductile PCCB with low equivalent compressive strength increased the ductility ratio of the beam to twice that of the control beam.The beam failed in pure flexure with considerable deformation capacity and without significant stiffness reduction.

Characteristics of the crack tip field in high-speed railway tunnel linings under train-induced aerodynamic shockwaves

High-speed railway tunnels in various countries have continuously reported accidents of vault falling concrete blocks.Once the concrete block falling occurs,serious consequences follow,and traffic safety may be endangered.The aerodynamic shockwave evolves from the initial compression wave may be an important inducement causing the tunnel lining cracks to grow and form falling concrete blocks.A joint calculation framework is established based on ANSYS Fluent,ABAQUS,and FRANC3D for calculating the crack tip field under the aerodynamic shockwave.The intensification effect of aerodynamic shockwaves in the crack is revealed,and the evolution characteristics of the crack tip field and the influence factors of stress intensity factor(SIF)are analyzed.Results show that(1)the aerodynamic shockwave intensifies after entering the crack,resulting in more significant pressure in the crack than the input pressure.The maximum pressure of the inclined and longitudinal cracks is higher than the corresponding values of the circumferential crack,respectively.(2)The maximum SIF of the circumferential,inclined,and longitudinal crack appears at 0.5,0.68,and 0.78 times the crack front length.The maximum SIF of the circumferential crack is higher than that of the inclined and longitudinal crack.The possibility of crack growth of the circumferential crack is the highest under aerodynamic shockwaves.(3)The influence of train speed on the SIF of the circumferential crack is more than 40%.When the train speed,crack depth,and crack length change,the change of pressure in the crack is the direct cause of the change of SIF.