Non-dimensional analysis on blast wave propagation in foam concrete:Minimum thickness to avoid stress enhancement

Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load.To investigate this interesting phenomenon,a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method.The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement.The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads,stress-strain relation and length of foam concrete are considered.In particular,the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed.Finally,non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data,which can provide a reference for the application of foam concrete in defense engineering.

Mechanical properties and associated seismic isolation effects of foamed concrete layer in rock tunnel

Foamed concrete has a good energy absorption capability and can be used as seismic isolation material for tunnels. This study aims to investigate the mechanical properties and associated seismic isolation effects of foamed concrete layer in rock tunnel. For this, a series of uniaxial/triaxial compression tests was conducted to understand the effects of concrete density, confining stress and strain rate on the mechanical properties of foamed concrete. The direct shear tests were also performed to investigate the effects of concrete density and normal stress on the nonlinear behaviors of foamed concrete layer-lining interface. The test results showed that the mechanical properties of foamed concrete are significantly influenced by the concrete density. The foamed concrete also has high volumetric compressibility and strain-rate dependence. The peak stress. residual stress. shear stiffness and residual friction coefficient of the foamed concrete layer-lining interface are influenced by the foamed concrete density and normal stress applied. Then, a crushable foam constitutive model was constructed using ABAQUS software and a composite exponential model was also established to study the relationship between shear stress and shear displacement of the interface, in which their parameters were fitted based on the experimental results. Finally, a parametric analysis using the finite element method(FEM) was conducted to understand the influence of foamed concrete layer properties on the seismic isolation effect, including the density and thickness of the layer as well as the shear stiffness and residual friction coefficient of the interface. It was revealed that lower density and greater thickness in addition to smaller shear stiffness or residual friction coefficient of the foamed concrete layer could yield better seismic isolation effect, and the influences of the first two tend to be more significant.

Preparation of High Performance Foamed Concrete from Cement,Sand and Mineral Admixtures

The titled high performance foamed concrete was developed from Portland cement, ultra fine granulated blast-furnace slag, pulverized fly ash and condensed silica fume by means of pre-foaming process. The resultant foamed concrete presents its thermal conductivity of about 0.16-0.75 W/（m·℃） and 28 d compressive strength of about 1.1-23.7 MPa when its mix proportion varies in the range of cement content 280 kg-650 kg/m^3, fly ash 42-97 kg/m^3, slag 64-146 kg/m^3, silica fume 34-78 kg/m^3, and sand 0-920 kg/m^3. The compressive strength of the foamed concrete with oven dried bulk density of 1500 kg/m^3 in appropriate mix proportion and with small amount of superplasticizer reached as high as 44.1 MPa. Meanwhile, the flesh foamed concrete behaves like an excellent flow-ability, therefore, is especially suitable for the application in case of massive foamed concrete casting in situ and in the case of filling casting into large volume underground irregular voids, except for pre-casting of building components like blocks, bricks, and wall panels.

Quantitative Analysis of Relationship Between Pore Structure and Compressive Strength of Foamed Concrete

The effect of dry density,water-cement ratio,the addition of fly ash,and sand content on the porosity and pore distribution of foamed concrete is investigated.Digital microscopy and Image J software are employed to examine the landscape of pores with different sizes.Based on the Balshin empirical formula,a mathematical model is established to quantitatively predict the relationship between the pore structures and the compressive strength of foamed concrete.The results well demonstrate that there is a significant correlation between the modified formula and empirical parameters.

Tests on Alkali-Activated Slag Foamed Concrete with Various Water-Binder Ratios and Substitution Levels of Fly Ash

To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.

Lateral compression and energy absorption of foamed concrete-filled polyethylene circular pipe as yielding layer for high geo-stress soft rock tunnels

Foamed concrete as energy absorption material for high geo-stress soft rock tunnels has been proven to be feasible due to its high compressibility and lightweight.However,the lengthy curing and defoaming problems caused by the cast-in-place method of large-volume foamed concrete remain unsolved.In this study,we propose a novel energy absorber composed of foamed concrete-filled polyethylene(FC-PE)pipe and analyze its deformation and energy absorption capacity via quasi-static lateral compression experiments.Results show that FC-PE pipes exhibit typical three-stage deformation characteristics,comprising the elastic stage,the plastic plateau,and the densification stage.Furthermore,the plateau stress,energy absorption,and specific energy absorption of the specimens are 0.81–1.91 MPa,164–533 J,and 1.4–3.6 J/g,respectively.As the density of the foamed concrete increases,the plateau stress and energy absorption increase significantly.Conversely,the length of the plastic plateau and energy absorption efficiency decrease.Moreover,based on the vertical slice method,progressive compression of core material,and the 6 plastic hinges deformation mechanism of the pipe wall,a theoretical calculation method for effective energy absorption is established and achieves good agreement with experimental results,which is beneficial to the optimization of the composite structure.

Study and application of a new type of foamed concrete wall in coal mines

A new type of airtight wall with the combination of foamed concrete and pier support was designed in this study. Based on the theories and models related to the foamed concrete and blasting shock load, using the numerical analysis method, this study obtains the new material＇s mechanical and destruction laws through analyzing its reaction to different conditions of load （mining and shock waves）, airtight wall thickness （1.2, 1.5, 1.8, 2.1 m） and steel pipe diameters （400, 450, 500 and 600 mm）. The results show that： ①foamed concrete can have very good suspension, and the pier column support is the main carrier of roof pressure; ② the damaged area of foamed concrete decreases as the foamed concrete thickness increases. Under impact loading, the thickness of the foamed concrete wall plays a more obvious role in retaining its integrity; ③under the same mining pressure, the damage area increases as the steel pipe diameter increases; ④ with additional mining stress increase, under whether static load or impact load, the stress on the foamed concrete and steel pipe will also increase gradually, therefore the actual airtight wall design will need to be based on specific circumstances in steel stress.

BIM-based construction technologies for precast foamed lightweight concrete wallboards

To promote the visualisation and informatisation of the construction process of precast foamed lightweight concrete wallboards(PFLCWs),from the analysis of the construction requirements of PFLCWs,three key construction technologies based on building information modelling(BIM),namely,parameterised modelling for the PFLCW layout design,drawing generation to draw the PFLCW layout and quantity statistics for extracting PFLCW quantities,are proposed.Then,a reinforced concrete(RC)frame infilled with PFLCW is considered the test model to verify the feasibility of the aforementioned technologies.The results show that PFLCW layout design can be accomplished rapidly and visually using parameterised modelling technology.The PFLCW layout diagram can be generated directly using drawing generation technology.The proposed quantity statistics technology enables the automatic export of PFLCW bills of quantities.The built parameterised model helps construction workers rapidly and intuitively understand the specific layout details of PFLCWs.Moreover,the generated layout drawing and the bills of quantities based on the parameterised model can guide the production and on-site installation of PFLCWs.The research conclusions can serve as a practical guide and technical support for PFLCW engineering applications.

In-situ Monitoring the Setting Behavior of Foamed Concrete Using Ultrasonic Pulse Velocity Method

The applicability of ultrasonic pulse velocity （UPV） method to in-situ monitor setting and hardening process of foamed concrete （FC） was systematically investigated. The UPVs of various FC pastes were automatically and continuously measured by a specially designed ultrasonic monitoring apparatus （UMA）. Ultrasonic tests were performed on FC mixtures with different density （300, 500, 800 and 1 000 kg/m3）, and different fly ash contents （0%, 20%, 40% and 60%）. The influence of curing temperatures （20, 40, 60 and 80~C） was also studied. The experimental results show that three characteristic stages can be clearly identified during the setting process of an arbitrary FC paste： dormant stage, acceleration stage, and deceleration stage. Wet density, fly ash content, and curing temperature have great impact on setting behavior. A stepwise increase of the wet density results in shorter dormant stage and larger final UPV. Hydration reaction rate is obviously promoted with an increase in curing temperature. However, the addition fly ash retards the microstn,lcture formation. To aid in comparing with the ultrasonic results, the consistence spread test and Vicat needle test （VNT） were also conducted. A correlation between ultrasonic and VNT results was also established to evaluate the initial and final setting time of the FC mixtures. Finally, certain ranges of UPV with reasonable widths were suggested for the initial and final setting time, respectively.

Computational Finite Element Modelling of Structural Behaviours of Precast Sandwiched Foamed Concrete Slab

The structural behaviour of Precast Lightweight Foamed Concrete Panel (PLFP) under flexural load is investigated by using ABAQUS 6.13. The PLFP is made up of two Whyte’s with a polystyrene insulator placed in between them using a double shear truss connector of diameter 6mm placed at an angle 45°. The panel is reinforced with both vertical and horizontal steel reinforcement of 9 mm diameter. Four panels with varying dimensions are simulated to investigate their Ultimate Strength and Load-deflection profile. The results show that the length to thickness ratio of the panel is the major contributing factor to the ultimate strength of the PLFP. From the load deflection curve, the panel with the least deflection has the highest thickness which also results in a high ultimate strength recorded at 34.43 KN.

Comparative Study of the Thermal and Mechanical Properties of Foamed Concrete with Local Materials

Living in a habitat with comfort is requested by all. Cinder block bricks have poor thermal properties, leading people to use fan heaters and air conditioners to regain comfort. To overcome this problem of thermal discomfort in buildings, we used lightweight concrete such as foamed concrete which is a material that has improved thermal properties for thermal comfort. In addition, this material was compared with local materials used for the construction of buildings such as BTC, adobe and BLT mixed with binders. The results showed that foamed concrete is a material that has good thermal and mechanical properties compared to local materials mixed with binders. The foamed concrete having acceptable thermo-mechanical properties was that having a density of 930 kg/m3. It has a thermal resistance of 0.4 m2·K/W for a thickness of 20 cm. The foamed concrete having acceptable thermo-mechanical properties was that having a density of 930 kg/m3. It has a thermal resistance of 0.4 m2·K/W for a thickness of 20 cm. For sunshine on a daily cycle equal to 12 hours, the characteristic thickness achieved by this material is 7.29 cm. It also has a shallow depth of heat diffusion having a lower thickness than other materials. This shows that foamed concrete is a promising material for the construction of buildings.

Hardening Properties of Foamed Concrete with Circulating Fluidized Bed Boiler Ash, Blast Furnace Slag, and Desulfurization Gypsum as the Binder

Recently, a large amount of circulating fluidized bed boiler ash (CFBA) and desulfurization gypsum (DSG) has been produced, and it is essential to develop technology to utilize them. These materials have CaO and SO3, which are considered to be a stimulant for blast furnace slag (BFS). This study presents an experimental investigation of the compressive strength and heavy metal ions immobilization properties of cement-free materials comprising CFBA, BFS, and DSG. The feasibility of manufacturing foamed concrete using these materials was examined, and field test of foamed concrete was conducted. Experimentally, the flow, compressive strength, and heavy metal ions concentration were evaluated via inductively coupled plasma atomic emission spectroscopy (ICP-AES) of the paste and foamed concrete. The experimental investigation revealed the self-healing hardening ability of fluidized bed boiler ash. In addition, the compressive strength was increased with the increasing replacement rates of BFS and DSG in the CFBA paste, and the compressive strength of 14.6 - 17.2 MPa was recorded over 28 days of curing. From the result obtained, the feasibility of manufacturing foamed concrete with a foam volume of 120 L, incorporating the aforementioned materials, is confirmed. It was also found that after 28 days of age, a 7.9-MPa compressive strength of the foamed concrete was attained, and heavy metal ions elution in this foamed concrete was also significantly reduced. Therefore, CFBA, BFS, and DSG could be used as a binder for the foamed concrete.

Experimental Investigation on Transmission of Stress Waves in Sandwich Samples Made of Foam Concrete

A series of impact tests of sandwich samples were completed using a large-diameter split Hopkinson pressure bar (SHPB)device at different velocities. The interlayer is made of foam concrete, loess or sand. The stress peak value decay, energy decay and waveform dispersion characters are studied by comparing the incident waves with the transmission waves. The tests indicate that the foam concrete has the best capabilities of shock resistance and energy absorption, the loess comes second, and the sand takes third place.

Development of a new type of foam concrete and its application on stability analysis of large-span soft rock tunnel

The long-term stability of large-span soft rock tunnel is influenced greatly by the creep effect of surrounding rock.The development of a new type of foam concrete which has the property of high compressibility and low ductility was introduced.And it was made as filling material of reserved deformation layer between the first lining and the second lining used in large-span soft rock tunnel.The effect of the new type of foam concrete was simulated as filling material of reserved deformation layer using numerical simulation.Through the comparison with the common large-span soft rock tunnel,the vault settlement and surrounding convergence are reduced by about 61% and 45%,respectively,after creep of 100 a.And in the second lining,the plastic zone reduces apparently and the maximum equivalent plastic strain decreases relatively.So,it can be found that the application of the new type of foam concrete as the filling material of reserved deformation layer can relieve the excessive force in second lining induced by rock creep,reduce its deformation and improve the stability of tunnel.

Shale Stone and Fly Ash Landfill Use in Landslide Hazardous Area in Sirnak City with Foam Concrete

Sirnak City and the surrounding areas are on steeper slopes. There are sliding large land masses or rocks. Underground water and harsh climatic conditions contain high risk hazard areas in urban living site with higher population density. In order to eliminate landslides and related events, significant precautions should be taken. The mapping of landslide risk may ease to take precautions. Even the application of landfill rock may reduce water content of soil. In this research, fly ash and Mine Waste shale stone were used with low density foam concrete. Waste mixture at certain proportions decreased cement use. Shale stone as fine aggregate instead of fly ash in specific proportions improved mechanical strength and porosity. Hence landslide hazardous area could be safer for urban living.

Optimization of construction machinery scheme of cast-in-situ concrete based on the improved scatter degree method

The basic requirement of mechanical construction of cast-in-situ concrete is that it could not only conduct quality qualification and safety production, but also achieve most economic benefits with less investment under the condition to meet the needs of project duration. Therefore, the selection of construction machinery scheme plays an important role. However, in the actual construction, it is usually that operators rely on their own experience and field conditions to determine the mechanics. Such a method is subjective and arbitrary, and it is not conducive to make the construction rationally. Considering the above reasons, an improved weight coefficient method was used to establish an estimation model to estimate the construction machinery scheme of cast-in-situ concrete, so as to make the procedure much rational.

PE纤维与细橡胶颗粒对泡沫混凝土弯曲韧性的影响

研究了聚乙烯(PE)纤维及其与细橡胶颗粒复掺对泡沫混凝土弯曲破坏模式、峰值强度、能量吸收特性和弯曲韧性的影响,并结合孔结构分析和微观形貌观察探究了其作用机理.结果表明:PE纤维使泡沫混凝土出现多缝开裂模式,显著提升了其峰值强度、能量吸收能力和弯曲韧性;复掺细橡胶颗粒可以进一步提升泡沫混凝土试件的比能量吸收和弯曲韧性;掺入PE纤维可以降低泡沫混凝土的平均孔径;复掺细橡胶颗粒导致泡沫混凝土试件的平均孔径增大,联通孔增多,对其峰值强度有不利影响;PE纤维及细橡胶颗粒提升泡沫混凝土弯曲韧性的主要原因在于其削弱了裂纹尖端的应力集中,同时增强了能量耗散作用.

聚酯纤维泡沫混凝土力学性能及孔结构研究

纤维的掺加可有效地改善泡沫混凝土抗压强度低、脆性特征显著的缺陷,增强其工程适用性。本工作针对聚酯纤维对泡沫混凝土力学性能的改善开展试验研究,选定密度等级为700 kg/m3的泡沫混凝土,考虑不同纤维体积掺量(0.1%、0.2%、0.3%和0.4%)对其抗压强度、抗折强度、劈裂抗拉强度以及延性的影响。结果表明:纤维掺量为0.1%时,材料表现出较优的抗压和劈裂抗拉性能,28 d强度分别增加了86.4%和91.3%;纤维掺量为0.2%时,材料表现出较优的抗折性能,28 d抗折强度提升了39.1%。试样破坏形态和应力-应变曲线表明,聚酯纤维可有效地提升泡沫混凝土的延性。最后,运用图像分析处理法分别获得了五组试件的孔结构参数,从细观孔结构的角度讨论了聚酯纤维对泡沫混凝土抗压强度的影响机理。

稻草纤维增强泡沫混凝土物理力学性能试验研究

为了研究稻草纤维增强泡沫混凝土的性能,以普通硅酸盐水泥为主要胶凝材料,硅灰、偏高岭土和粉煤灰为辅助胶凝材料,稻草纤维为增强材料,采用物理发泡法制备纤维增强泡沫混凝土;通过全因子试验,研究在不同水胶比和发泡剂掺量下,稻草纤维掺量对泡沫混凝土的密度、吸水率、抗压强度、抗折强度、劈裂抗拉强度和抗冻性能的影响。结果表明:对于不同水胶比和发泡剂掺量,泡沫混凝土的密度、抗压强度和劈裂抗拉强度均随纤维掺量的增加呈现出先增加后降低的变化规律;抗压强度随密度增加呈幂函数增加关系;劈裂抗拉强度随抗压强度的增加呈指数函数增加关系;当水胶比为0.45时,抗折强度随纤维掺量的增加先增加后降低,当水胶比为0.50时,抗折强度随纤维掺量的增加而增加;纤维的掺入增大了泡沫混凝土的泡孔尺寸和吸水率,降低了其抗冻性能。