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Abstract

Characterizing material strength in-situ for existing structures poses a major problem for a range of civil engineering applications including structural modelling for tunnelling-vulnerability assessment and pre-earthquake resiliency evaluation, especially for unreinforced masonry buildings. Present methods require expensive testing equipment often requiring access to the structure and possible destruction of historic material. This article introduces spectrometry as a non-destructive means for identifying different brick clays and their firing levels, both of which influence the masonry’s mechanical behavior. The experiments herein considered bricks of 2 clay groups (red and yellow) fired at 3 kiln temperatures (700ºC, 950ºC, 1,060ºC). Samples were examined via spectrometry within the short-wave infrared range (1,300–2,200 nm). A Partial Least Square Discriminant Analysis (PLSDA) model was calibrated using 96 samples and tested on a set of 48 samples, resulting in a 98% success rate in classification of the two clay types and a 100% success rate for classification among the 3 firing levels. The ability of the PLSDA model to reliably distinguish well-fired bricks from other samples, irrespective of raw material configuration, shows the potential to use this approach as a new, non-destructive means for in-situ assessment of brick for architectural conservation, as well as for safety and serviceability assessments.

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... This indicates the higher sensitivity of the hyperspectral technique, as well as its capability to detect variability within a material class. Initial work exploring intraclass material distinction was established previously by the authors for brick [51], mortar [52], and concrete [53]. ...
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... Specifically, hyperspectral imaging is an effective tool to estimate the mechanical and chemical properties of construction materials. In [1], spectrometry data was used to determine bricks characteristics. In [2], concrete and cement-based materials with different water to cement ratio (w/c) were characterized by hyperspectral imaging. ...
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Infrared thermography (thermal imaging) is an important and powerful technique for consideration when investigating any structural situation where a ready source of surface heating (or cooling) is available, or where the item under investigation itself supplies such conditions. The methods used are totally non-destructive and non-invasive, and can be highly cost-effective. This paper explores a wide range of applications; particularly relating to structural investigation situations. Some guidance is given on optimum timing, conditions and viewing locations for the various situations described as well as limitations of the technique.
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PLS-regression (PLSR) is the PLS approach in its simplest, and in chemistry and technology, most used form (two-block predictive PLS). PLSR is a method for relating two data matrices, X and Y, by a linear multivariate model, but goes beyond traditional regression in that it models also the structure of X and Y. PLSR derives its usefulness from its ability to analyze data with many, noisy, collinear, and even incomplete variables in both X and Y. PLSR has the desirable property that the precision of the model parameters improves with the increasing number of relevant variables and observations.This article reviews PLSR as it has developed to become a standard tool in chemometrics and used in chemistry and engineering. The underlying model and its assumptions are discussed, and commonly used diagnostics are reviewed together with the interpretation of resulting parameters.Two examples are used as illustrations: First, a Quantitative Structure–Activity Relationship (QSAR)/Quantitative Structure–Property Relationship (QSPR) data set of peptides is used to outline how to develop, interpret and refine a PLSR model. Second, a data set from the manufacturing of recycled paper is analyzed to illustrate time series modelling of process data by means of PLSR and time-lagged X-variables.
Article
The changes in brick porosity upon firing (700 up to 1100 °C) and its relation to the mineralogical composition are examined. Two types of raw clay with a composition representative of that used in brick-making industry were selected to manufacture the bricks: one contains notable amounts of carbonates, with a grain size of under 1 mm, and the other is predominantly quartzitic and lacking in carbonates. We demonstrate that the presence or absence of carbonates strongly influences the porosity development and, therefore, the brick texture and physical-mechanical properties. The carbonates in the raw clay promote the formation of fissures and of pores under 1 μm in size when the bricks are fired between 800 and 1000 °C. The absence of carbonates results in a continuous reduction in porosity and a significant increase in the pore fraction with a radius (r)>1 μm as the firing temperature rises and smaller pores coalesce. Porosity and pore size distribution results obtained from the combined use of hydric tests (HT), mercury intrusion porosimetry (MIP) and digital image analysis (DIA) of scanning electron microscopy photomicrographs are compared. A clear correlation between the water absorption and drying behaviour of the bricks and the porosity plus pore size distribution is observed. DIA discloses the evolution of size, shape and connectivity of macropores (r> 1 μm) and evidences that MIP results underestimate the macropore content. Conversely, MIP gives a good estimate of the open porosity and of the distribution of pores with r<1 μm. It is concluded that the combined use of these complementary techniques helps to fully characterise the pore system of bricks. These results as well as the study of the evolution of the speed of ultrasound waves vs. time yield useful information to evaluate the bricks physical–mechanical behaviour and durability. The relevance of these findings in the conservation of historic buildings is discussed.
Article
Portable linear accelerator systems are being used to provide high-intensity X-rays for structural engineering studies and non-destructive testing in the USA and Europe. These devices greatly enhance the ability of engineers to examine structural members for hidden defects, as well as to study internal design and construction details of large buildings, bridges, parking garages and other structures, including steel memebers up to 16" thick and concrete over 62" thick. The resulting radiographic images are of excellent quality, enabling quick, reliable analysis of hidden conditions in the field. Three representative case studies are discussed in detail, and new developemnts are highlighted, including use of robotics for positioning and the use of accelerators for curing composite materials in-situ.
Article
A tutorial on the partial least-squares (PLS) regression method is provided. Weak points in some other regression methods are outlined and PLS is developed as a remedy for those weaknesses. An algorithm for a predictive PLS and some practical hints for its use are given.
Article
The reflectance spectra of minerals are studied as a function of spectral resolution in the range from 0.2 to 3.0 microns. Selected absorption bands were studied at resolving powers as high as 2240. At resolving powers of approximately 1000, many OH-bearing minerals show diagnostic sharp absorptions at the resolution limit. At low resolution, some minerals may not be distinguishable, but as the resolution is increased, most can be easily identified. As the resolution is increased, many minerals show fine structure, particularly in the OH-stretching overtone region near 1.4 micron. The fine structure can enhance the ability to discriminate between minerals, and in some cases the fine structure can be used to determine elemental composition.
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ASTM C597-97 standard test method for pulse velocity through concrete
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ASTM C62-00 standard specification for building brick (solid masonry units made from Clay or Shale)
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ASTM International. 2001. ASTM C62-00 standard specification for building brick (solid masonry units made from Clay or Shale). West Conshohocken, PA: ASTM International. doi:10.1520/C0062-00.
ASTM C1196-14a standard test method for in-situ compressive stress within solid unit masonry estimated using flatjack measurements
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ASTM International. 2014a. ASTM C1196-14a standard test method for in-situ compressive stress within solid unit masonry estimated using flatjack measurements. West Conshohocken, PA: ASTM International. doi:10.1520/ C1196-14A.
ASTM C1197-14a standard test method for in-situ measurement of masonry deformability properties using the flatjack method
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ASTM International. 2014b. ASTM C1197-14a standard test method for in-situ measurement of masonry deformability properties using the flatjack method. West Conshohocken, PA: ASTM International. doi:10.1520/C1197-14A.
ASTM C1531-16 standard test methods for in-situ measurement of masonry mortar joint shear strength index
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ASTM International. 2016. ASTM C1531-16 standard test methods for in-situ measurement of masonry mortar joint shear strength index. West Conshohocken, PA: ASTM International. doi:10.1520/C1531-16.
Numerical modeling of ground-penetrating radar (GPR) for the investigation of jointing defects in brick masonry structures
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Hamrouche, R., G. Klysz, J.-P. Balayssac, S. Laurens, J. Rhazi, G. Ballivy, and G. Arliguie 2009. Numerical modeling of ground-penetrating radar (GPR) for the investigation of jointing defects in brick masonry structures. Proceedings of the 7th International Symposium on Nondestructive Testing in Civil Engineering NDTCE 9, Paper 96. Retrieved from http://www.ndt.net/article/ ndtce2009/toc.htm
NDE techniques for concrete and masonry structures
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Popovics, J. S. 2003. NDE techniques for concrete and masonry structures. Progress in Structural Engineering and Materials 5 (2):49-59. doi:10.1002/(ISSN)1528-2716.
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