The naive building economics manifesto

From research performed for two recent evaluation studies, the author translates to building economics the concepts lately introduced in naive physics. He argues that expert systems designed to advise the user in the early project planning‐design stage should be able to employ both basic economic principles and qualitative commonsense reasoning about the likely direction of change of the key variables considered, since the time factor is crucial. A toy expert system dealing with interest rate trends is analysed to show some feasible strategies that could be implemented The author is Assistant Professor of Economics in Architecture at Massachusetts Institute of Technology.     

Moisture buffering capacity of highly absorbing materials

This research investigates the possibility to use highly absorbing materials to dampen indoor RH% variations. The practical MBV of sodium polyacrylate, cellulose-based material, perlite and gypsum is evaluated for a daily cyclic exposure that alternates high (75%) and low (33%) RH% levels for 8 h and 16 h, respectively. The adjustment velocity to RH% variations and the presence of hysteretic phenomena are also presented. The cellulose-based material proves to be the most suitable for moisture buffering applications. Starting from this material’s properties, the effect of thickness, vapour resistance factor (μ) and mass surface exchange coefficient (Z_v) on sorption capacity is evaluated by the use of a numerical model.     

Average permeability measurements for an individual dwelling in Romania

The air permeability represents that feature of the building playing a major role in both the building energy performance and the indoor environment quality, therefore its prediction is very important. The statistical prediction models which are used today on a very large scale present large errors. The experimental measurements correct this deficit, but they are impossible to be carried out for large apartment building due to technical concerns. In this study we propose an intermediate approach “the prediction of average permeability as a weighted mean of the different measured permeabilities characteristic to the different types of joinery”. The article presents the mathematical models and the adapted experimental protocol for four different parameters that describes the permeability. The experimental work was carried out for an apartment placed at the ground level of a two storey house in Romania. The proposed approach presents smaller errors: 5% for the overall leakage airflow and 15% for the average permeability. The study presents interesting data being among the first permeability measurements in Romania. The originality of the study is also given by the proposed model which is oriented towards large dimensions blocks of apartments.     

Moisture response of building facades to wind-driven rain: Field measurements compared with numerical simulations

Wind-driven rain (WDR) is one of the most important boundary conditions governing the hygrothermal behaviour of building facades, which is usually numerically analysed with the so-called Heat-Air-Moisture (HAM) transfer models. In the traditional approach of HAM transfer models, WDR is implemented in a simplified manner: the total mass of all raindrops impinging on a certain surface area of a building facade during the time interval of the meteorological input data (typically 1 h) is spatially and temporally averaged and is supplied to the facade as an averaged moisture flux. However, real WDR is the sum of individual raindrops that impinge on the facade in a spatially and temporally discrete modus, and that do not only spread at impact, but may also splash or bounce off the facade. Therefore the reliability of this simplification can be questioned. To investigate its validity, a new experimental set-up was developed at a full-scale test building. It allows simultaneous and continuous measurements of the reference wind speed and direction, WDR intensity, outdoor air temperature and humidity, as well as the response of facade material samples to these environmental conditions. For this purpose, a measuring device was developed that monitors the weight change of the sample with a resolution of 5 mg. Temperatures at the interior and exterior material surfaces are also monitored. The whole measurement data set is used to check the validity of the traditional numerical approach. Large differences are found between the measurement and simulation results, which cannot solely be attributed to the uncertainty in the convective moisture transfer coefficient, but may be due to two additional reasons: the occurrence of splashing and bouncing at raindrop impact on the facade, which is not included in the model, and/or errors in surface moisture evaporation and absorption due to modelling the actual random and discrete raindrop impingement as a simplified averaged moisture flux.     

Pore fabric shape anisotropy in porous sandstones and its relation to elastic wave velocity and permeability anisotropy under hydrostatic pressure

To understand the relationship between pore space anisotropy and petrophysical properties, we developed a novel apparatus capable of simultaneously measuring permeability, porosity and ultrasonic velocities at hydrostatic pressures up to 100 MPa. First, we use magnetic susceptibilities and acoustic wave velocities to identify the principal anisotropy axes under ambient laboratory conditions. This directional anisotropy data is then used to guide experiments on two sandstones (Bentheim and Crab Orchard) under hydrostatic pressure from 5 to 90 MPa. We find the structural anisotropy formed by the void space is well described by velocity anisotropy in both cases. Under hydrostatic pressure, the acoustic anisotropy of Crab Orchard sandstone (COS) decreases from 3% and 7% at 5 MPa (P-wave and S-wave) to 1.5% and 1%, respectively, at effective pressures over 40 MPa; for Bentheim sandstone the decrease is considerably less. Permeability of COS is 125×10⁻¹⁸ m², decreasing rapidly as effective pressure increases, with permeability parallel to bedding approximately twice that normal to bedding. In contrast, permeability of Bentheim sandstone is 0.86×10⁻¹² m², and varies little with effective pressure or coring direction. We relate many of our measurements made under hydrostatic pressure to the contrasting pore fabric between the two rock types, and infer that a critical pressure is required for the initiation of crack closure.     

Comparison of Northern Ireland radon maps based on indoor radon measurements and geology with maps derived by predictive modelling of airborne radiometric and ground permeability data

Publicly available information about radon potential in Northern Ireland is currently based on indoor radon results averaged over 1-km grid squares, an approach that does not take into account the geological origin of the radon. This study describes a spatially more accurate estimate of the radon potential of Northern Ireland using an integrated radon potential mapping method based on indoor radon measurements and geology that was originally developed for mapping radon potential in England and Wales. A refinement of this method was also investigated using linear regression analysis of a selection of relevant airborne and soil geochemical parameters from the Tellus Project. The most significant independent variables were found to be eU, a parameter derived from airborne gamma spectrometry measurements of radon decay products in the top layer of soil and exposed bedrock, and the permeability of the ground. The radon potential map generated from the Tellus data agrees in many respects with the map based on indoor radon data and geology but there are several areas where radon potential predicted from the airborne radiometric and permeability data is substantially lower. This under-prediction could be caused by the radon concentration being lower in the top 30 cm of the soil than at greater depth, because of the loss of radon from the surface rocks and soils to air.     

Investigations of water inrushes from aquifers under coal seams

In many coal mines, limestone-confined aquifers underlie coal seams. During coal extraction from these mines, water inrushes occur frequently with disastrous consequences. This paper introduces the hydrogeological conditions of the coal mines and the potential water inrush disasters from aquifers under coal seams. It then presents the water inrush mechanism. The main factors which control water inrushes include strata pressure, mining size, geologic structures and the water pressure in the underlying aquifer. Analysis shows that reduction of confinement due to mining is the major cause of the water-conducting failure in the floor strata. The depth of the failure zone is strongly dependent on the mining width. This paper also presents field observation results of the water-conducting failure in the floor strata, and applies the finite element method coupled with stress-dependent permeability to analyze hydraulic conductivity enhancement due to coal extraction. Finally, theoretical and empirical methods to predict water inrushes are given, and technical measures for improving mine design and safety for coal extraction over aquifers are presented. These measures include fault and fracture grouting and mining method modification such as changing long-wall to short-wall mining.     

Moisture buffering and effect of ventilation rate and volume rate of hygrothermal materials in a single room under steady state exterior conditions

In this paper, experiments and simulations investigating the moisture buffering of the gypsum boards are described. A test chamber was used for the experiments. The gypsum board was installed on the interior surface in the test chamber. This chamber was located in a climate chamber. The ambient condition of the chamber was controlled at constant temperature and humidity. In the experiment three cases of ventilation rate, no ventilation, 1.0 air change per hour and 5.0 air changes per hour, were investigated. In the experiment the relationship between moisture buffering and volume rate of the materials, various area and locations of the gypsum boards on the surrounding walls were investigated.     

Experimental study on permeability and porosity evolution of host rock with varying damage degrees in excavation damaged area under real-time ultra-high temperature and triaxial stress/seepage pressure condition

Bulletin of Engineering Geology and the Environment - In the field of high-temperature underground excavations, previous scholars often focused on the seepage characteristics of intact host rock...     

常压下水泥粒度和水胶比对混凝土渗透性的影响

试验测试了混凝土在常压状态下,不同水泥粒度和水胶比对混凝土渗透性的影响。指出在一定气干条件下,水泥粒度越细,水胶比越低,混凝土在毛细孔压力作用下的渗透性越大。尤其是掺入了超细矿渣的水泥混凝土。这种渗透性的增大更为明显。     

泥水盾构带压开舱时泥膜的微观孔隙及渗透性研究

泥膜的良好闭气性是保证泥水盾构带压开舱安全顺利实施的关键之一,要想提高泥膜的闭气性,首先应了解泥膜在带压开舱过程中的孔隙结构及渗透性变化。以南京纬三路过江通道在江底砂卵石地层中进行带压开舱为背景,在自制的试验装置中进行泥浆成膜和泥膜闭气试验,然后观测泥膜的孔隙结构和孔径变化,最后分析泥膜渗透系数的变化。研究结果表明:试验泥浆在0.2 MPa气压作用下6 h,在试验地层表面形成的泥膜厚度约为5.0 mm、孔隙率约为67%,在闭气过程中泥膜会发生压缩,且第一次单位压力引起的压缩量最大;随着闭气压力的增大,大孔隙组被优先压缩;泥膜基本单元体为骨架状结构,孔隙主要是粒间孔隙与架空孔隙,孔隙分布不连续、连通性差;孔径分布范围较广,其中在0.1~3.0μm的孔隙组占有绝对优势;本次试验中压缩后泥膜的渗透系数在10-9 cm/s量级。研究结果有助于明确泥膜在闭气过程中的变化,对后续提高泥膜闭气性的研究有重要的参考意义。     

Vibration of a thin-walled carbon fibre corrugated circular cylinder under external water pressure

The paper reports on a theoretical and an experimental investigation carried out on a thin-walled corrugated carbon fibre circular cylinder in air and also under external water pressure. This corrugated circular cylinder was invented by Ross in 1987.The theoretical investigation was carried out using the finite element analysis to model both the structure and the fluid. The theoretical investigation used two different programs, one of which was the giant computer program ANSYS and the other was an in-house program developed by Ross and Little. For the shell structure, the ANSYS program used two different doubly curved thin-walled shell elements, while the in-house program used a simpler axisymmetric thin-walled shell element. This axisymmetric element allowed a sinusoidal variation of the displacements in the circumferential direction, thus, decreasing preparation and computational time. Agreement between the different finite elements was found to be quite good. The investigation also found that there was good correlation between experiment and theory for the in-house software, but was a little disappointing when using ANSYS. Errors may, however, have occurred with the experimental results, as the model was hand-made and neither its geometry nor its material properties were perfect. It was found particularly encouraging for the in-house software to give better results than ANSYS, as the in-house software only took a few hours to set up the computer model, and a few seconds to analyse the vessel, whereas the ANSYS software took several weeks to set up the computer model, and several minutes to analyse the shell. The ANSYS software, however, did have the advantage in producing excellent graphical displays in both the pre-processing and post-processing modes.     

Theoretical and experimental study of external water pressure on tunnel lining in controlled drainage under high water level

To reduce environmental effects due to free tunnel drainage, a controlled drainage scheme is proposed for tunnels under high water level, for which there is no code provision for tunnel design. A suitable structure form is suggested and the distribution of water pressure on tunnel lining is studied by theoretical analysis, indoor test and field measurement. The study indicates that the grouting zone cannot reduce water pressure on lining with complete waterproofing, only when drainage measure is taken can the grouting zone be effective in reducing water pressure on lining. It is also shown that there exists an optimum size for grouting zone, increase of the size of grouting zone may not unlimitedly reduce the water pressure on lining.     

Various admixtures to mitigate the long-term strength retrogression of Portland cement cured under high pressure and high temperature conditions

In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature (HPHT) curing conditions, various influencing factors, including cement sources, particle sizes of silica flour, and additions of silica fume, alumina, colloidal iron oxide and nano-graphene, were investigated. To simulate the environment of cementing geothermal wells and deep wells, cement slurries were directly cured at 50 MPa and 200 °C. Mineral compositions (as determined by X-ray diffraction Rietveld refinement), water permeability, compressive strength and Young's modulus were used to evaluate the qualities of the set cement. Short-term curing (2–30 d) test results indicated that the adoption of 6 μm ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems, while the addition of silica fume had a detrimental effect on strength stability. Long-term curing (2–180 d) test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems. However, none of the admixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases.