Dosagem científica de concretos estruturais contendo agregado miúdo de resíduo de concreto

Studies are being carried out around the world aiming at the reuse of construction and demolition waste (CDW). Special attention has been given by the researchers to the coarse fraction of recycled concrete aggregates (RCA). However, when the concrete residues are processed to obtain the coarse aggregates, a large amount of fine aggregate (FRCA) is generated depending on the origin of the residue. As the studies on the use of FRCAs in structural concrete are scarce, the present work aims the mix design of concrete of resistance classes C30 and C60 containing different levels (0, 25% and 50%) of recycled sand obtained from concretes of different origins. The sources of concrete residues for the production of RCAs were: (i) laboratory-produced concrete residue (LAB) and (ii) concrete residue obtained from demolition (D). For the mix design of the concretes the Compressible Particle Packing Model (CPM) was used and adapted to take into account the different water absorption capacities of the FRCAs used. As the FRCAs have different amount of attached paste in their composition, the paste volume was determined by immersion of the aggregates in acid and correlated that volume with the density and water absorption of the particles. The concretes produced with FRCA showed mechanical properties practically equal to the reference concretes. Total and capillary absorption were higher for concretes containing Sand D (higher water absorption). Drying shrinkage and chloride ions penetration were higher for recycled concrete, and the higher the AMRC content in the mixtures (mainly from Sand D), the more expressive the increase. The CPM showed to be quite adequate for the mix design of concrete containing different FRCAs.Estudos estão sendo realizados em todo o mundo visando o reaproveitamento dos resíduos de construção e demolição (RCD). Tem recebido especial atenção dos pesquisadores a fração graúda dos agregados reciclados de concreto (ARC). Ocorre que ao se processar os resíduos de concreto para obtenção dos agregados graúdos, gera-se, dependendo da origem do resíduo, grande quantidade de agregado miúdo (AMRC). Como são escassos os estudos sobre o uso das AMRCs em concretos estruturais, o presente trabalho visa a dosagem científica de concretos de classes de resistência C30 e C60 contendo diferentes teores (0, 25% e 50%) de areia reciclada obtidas de concretos de diferentes origens. As fontes de resíduos de concreto para produção dos ARCs foram: (i) resíduo de concreto produzido em laboratório (LAB) e (ii) resíduo de concreto obtido de demolição (D). Para a dosagem dos concretos utilizou-se o Modelo de Empacotamento Compressível de partículas (MEC) que foi adaptado para que se levasse em consideração as diferentes capacidades de absorção de água dos AMRCs utilizados. Como os AMRCs possuem diferentes quantidade de pasta aderida na sua composição, determinou-se o volume de pasta através da imersão dos agregados em ácido e correlacionou-se esse volume com a densidade e absorção da água das partículas. Os concretos produzidos com AMRC, apresentaram propriedades mecânicas praticamente iguais aos concretos de referência. Absorção total e por capilaridade foram superiores para os concretos contendo Areia D (de maior absorção de água). A retração por secagem e a penetrabilidade de íons cloretos foram maiores para os concretos reciclados, sendo mais expressivo o acréscimo quanto maior o teor de AMRC nas misturas (principalmente da Areia D). O MEC mostrou-se adequado para a dosagem dos concretos contendo as diferentes AMRCs

Generalized quality control parameter for heterogenous recycled concrete aggregates: A pilot scale case study

Although Recycled Concrete Aggregates, RCAs, derived from concrete waste, represent a potential sustainable solution for the structural concrete production, their heterogeneous composition is a feature that still prevents their large-scale use in the construction industry all around the world. In order to find a possible existing relationship between the source of residues and the resulting RCAs characteristics, a pilot scale case study was carried out, in which approximately 20 tons of concrete waste, derived from different origins, were processed to obtain granulometric fractions from coarse aggregates to powders. The RCAs fractions, obtained using a controlled processing procedure, were then thoroughly characterized to establish quality control parameters that could lead to a classification of different types of recycled aggregate generated. The results show that the source of concrete waste strongly influences the amount of each aggregate fraction produced during processing and, aggregate properties were dependent on the waste origin. Despite this, the presented analysis demonstrated, that by evaluating a fundamental parameter such as the Attached Paste/Mortar within the RCAs, a generalized quality-control classification can be proposed for the industrial upscaling of RCAs characterization. It is believed that such a classification could promote the integral and rational re-use of these secondary raw materials in different cement based products of the construction sector

Deregulated sex chromosome gene expression with male germ cell-specific loss of dicer1.

MicroRNAs (miRNAs) are a class of endogenous, non-coding RNAs that mediate post-transcriptional gene silencing by inhibiting mRNA translation and promoting mRNA decay. DICER1, an RNase III endonuclease encoded by Dicer1, is required for processing short 21-22 nucleotide miRNAs from longer double-stranded RNA precursors. Here, we investigate the loss of Dicer1 in mouse postnatal male germ cells to determine how disruptions in the miRNA biogenesis pathway may contribute to infertility. Reduced levels of Dicer1 transcripts and DICER1 were confirmed in germ cell knock-out (GCKO) testes by postnatal day 18 (P18). Compared to wild-type (WT) at 8 weeks, GCKO males had no change in body weight; yet showed significant reductions in testis mass and sperm number. Histology and fertility tests confirmed spermatogenic failure in GCKO males. Array analyses at P18 showed that in comparison to WT testes, 75% of miRNA genes and 37% of protein coding genes were differentially expressed in GCKO testes. Among these, 96% of miRNA genes were significantly down-regulated, while 4% miRNA genes were overexpressed. Interestingly, we observed preferential overexpression of genes encoded on the sex chromosomes in GCKO testes, including more than 80% of previously identified targets of meiotic sex chromosome inactivation (MSCI). Compared to WT, GCKO mice showed higher percentages of germ cells at early meiotic stages (leptotene and zygotene) but lower percentages at later stages (pachytene, diplotene and metaphase I) providing evidence that deletion of Dicer1 leads to disruptions in meiotic progression. Therefore, deleting Dicer1 in early postnatal germ cells resulted in deregulation of transcripts encoded by genes on the sex chromosomes, impaired meiotic progression and led to spermatogenic failure and infertility

Meiotic spreads show deletion of <i>Dicer1</i> disrupts progression of meiosis I.

<p>(A) It was possible to identify the 5 sub-stages of meiosis I by combining the reactivity patterns of two antibodies against synaptonemal complex protein 3 (SYCP3) and γH2AX. SYCP3 is a protein essential for synapsis of homologous chromosomes and γH2AX localizes to double-strand breaks and XY bodies during meiosis. A total of 200 spreads were counted in testis cell preparations from WT and GCKO mice at P22. (B) Chi square analysis shows GCKO testes contained significantly higher numbers of germ cell spreads at the leptotene and zygotene stages of meiosis I and fewer spreads at pachytene, diplotene and metaphase I stages (<i>P</i><0.001), suggesting that the loss of <i>Dicer1</i> lead to disruptions in progression through meiosis I.</p

Levels of <i>Dicer1</i> transcripts and DICER1 protein in GCKO testis samples are significantly reduced by P18.

<p>(A) In comparison to WT testes, real-time qRT-PCR shows a 6-fold reduction in <i>Dicer1</i> RNase III endonuclease transcripts in GCKO testes by P18 (*<i>P</i>  = 0.018). (B) Western blot analysis using rabbit antibody against the N-terminal helicase domain of DICER1 and HRP-conjugated goat anti-rabbit IgG antibody shows reduced protein expression in GCKO testes by P18. The arrows point to the 217 kDa DICER1 protein and to the equivalent loading of 50 kDa protein from WT and GCKO testes. (C) Immunofluorescence detection of DICER1 protein in WT and GCKO testes at P18 using the same antibody used for western blotting. In WT sections, DICER1 localizes to the cytoplasm of most cell types populating the P18 testis, including Sertoli cells, spermatogonia and spermatocytes. At this developmental time point, secondary spermatocytes and spermatids are not present. In the P18 GCKO testis sections, DICER1 appears primarily in the cytoplasm of Sertoli cells located near the basement membrane with scant detection of DICER1 protein in the cytoplasm of spermatogonia and pachytene spermatocytes (magnification  = 40x). (D) Cross sections of WT and GCKO testes on P18 stained with HE show no major differences in cellular composition suggesting that the changes in in <i>Dicer1</i> transcript and protein levels in the GCKO testes were not explained by differences in cell populations.</p

Number of miRNAs and mRNAs up- or down-regulated for each chromosome in GCKO testes on P18. Data for miRNA and mRNA are expressed on a per chromosome basis and reported for those probe sets with intensities that could be scored as increased, decreased or no change in GCKO when compared to WT testes.

<p>Number of miRNAs and mRNAs up- or down-regulated for each chromosome in GCKO testes on P18. Data for miRNA and mRNA are expressed on a per chromosome basis and reported for those probe sets with intensities that could be scored as increased, decreased or no change in GCKO when compared to WT testes.</p

Failure of meiotic sex chromosome inactivation (MSCI) in P18 <i>Dicer1</i> GCKO testes.

<p>A) Pie charts show the number of genes that are normally silenced during MSCI that were detected by array overlaid with the percentages of X- and Y-genes in GCKO testes with expression levels that were either significantly up-regulated (83.8% and 100%, respectively) or not changed (16.2 and 0%, respectively. B) Bar graph showing the number of overexpressed (>1.5 RFC) X- and Y-genes with or without binding sites for miRNAs shown to be deregulated in P18 GCKO testes. The majority of overexpressed genes (102/123 = 82.9%) contain recognition sites for deregulated miRNAs.</p

Histology comparing WT and GCKO seminiferous tubules and epididymides at 5, 8 and 10 weeks.

<p>(A) In comparison to WT seminiferous tubules at 5 weeks, GCKO sections show tubules with increased lumen diameters and few elongating and elongated spermatids (*). By 8 weeks, cross sections from GCKO testes show prominent pynotic cells (arrows) and reduced numbers of elongating and elongated spermatids. By 10 weeks, cross sections of GCKO testes show further enlargement of tubule lumens and absence of elongating spermatids in the majority of tubules. (B) Epididymides of WT mice at 5 weeks and GCKO mice at 5, 8 and 10 weeks showing reduced sperm numbers in epididymides of knockout mice by 5 weeks and the absence of mature spermatozoa in GCKO epididymides at the 8 and 10 week timepoints.</p

GCKO mice show reduced testis weight and sperm number, abnormal sperm morphology and infertility.

<p>(A) Body and testis weights were measured in WT and GCKO males at P22, 5 and 8 weeks (at each time point, n = 5 for WT and n = 5 for GCKO). In comparison to WT, GCKO males had no change in body weight over 8 weeks, yet showed significant reductions in testis weight as early as 5 weeks and remained so at 8 weeks (*both <i>P</i>≤0.004). Values represent the mean ± SEM. (B) In comparison to WT, GCKO epididymal sperm counts revealed significant reductions in sperm number by 8 weeks (**<i>P  = </i>0.0003). Approximately 80% of WT and less than 10% of GCKO epididymal sperm showed normal head and tail morphologies as represented in the photomicrographs taken at 40x. (C) Fertility testing showed that 4–6 month old GCKO males were unable to sire litters in comparison to littermate controls when mated 3–6 times with 12-week fertile B6CBAF1/J females.</p