Durability of Laterized Concrete Exposed to Sulphate Attack Under Drying-Wetting Cycles.

The study investigated the performance of laterized concrete exposed to drying-wetting cycles of sulphate environments with a view to providing empirical data for laterized concrete specification.  It adopted accelerated ageing method to investigate the effect of sulphate attack on laterized concrete exposed to wetting-drying cycle comprising of 4 days of full immersion and 3 days of drying at ambient temperature at two concentrations (3% and 5%) of magnesium sulphate solution for a total exposure period of 24 weeks.  The test cubes were first cured by complete immersion in water for 28 days and afterward exposed to wetting-drying cycle of magnesium sulphate solution. The compressive strength was determined by using an ELE 2000kN compression testing machine. Data obtained from the experiments were analysed using percentages, mean, ANOVA and regression analysis. The results of the tests carried out showed that conventional concrete had a better resistance (in terms of compressive strength) to sulphate attack than laterized concrete. Conventional concrete exposed cyclically to sulphate solution of concentrations of 3% and 5% lost 18.91% - 30.34% of its compressive strength, after a period of 24 weeks of exposure. Whereas, laterized concrete similarly exposed for the same period; lost 26.54% - 31.79% (at 20% laterite content) and 36.67% - 51.33% (at 40% laterite content) of its compressive strength. It showed that the compressive strength of the tested laterized concrete specimen decreased significantly between 10% and 50%, each at ? = 0.05 with increasing sulphate concentration, laterite content and exposure period. The study concluded that conventional concrete performed better than laterized concrete in intermittently sulphate-laden environments. Keywords: Laterized concrete, Sulphate, Durability, Compressive strength

Durability of Ternary Blended Cement Concrete in Sulphuric Acid

This study investigated the durability of concrete made of ordinary Portland cement (OPC), bamboo leaf ash (BLA) and pulverized burnt clay waste (PBCW) as binders in sulphate environment. Ternary blending of OPC, BLA and PBCW at ten (10) levels (100:0:0; 90:5:5; 90:10:0; 90:0:10; 80:5:15; 80:10:10; 80:15:5; 70:10:20; 70:15:15; 70:20:10) were used in producing 480 concrete cubes of size 100 mm and cured for 28 days in water. Further exposure to sulphuric acid (H2SO4) of 0, 1, 3 and 5% concentrations was done for a maximum of 120 days. Strength deterioration factors were thereafter calculated as a measure of acid attack resistance for the blended cement concrete. Results show that concrete containing PBCW and BLA performed better in H2SO4 than that of the control. Therefore, it can be concluded that the incorporation of BLA and PBCW in concrete improved its durability in sulphate laden environment. Keywords:durability, sulphuric acid, bamboo leaf ash, pulverized burnt clay waste, strength deterioration

High cases of submicroscopic Plasmodium falciparum infections in a suburban population of Lagos, Nigeria.

BACKGROUND: Asymptomatic malaria parasites are significant sources of infections for onward malaria transmission. Conventional tools for malaria diagnosis such as microscopy and rapid diagnostic test kits (RDT) have relatively low sensitivity, hence the need for alternative tools for active screening of such low-density infections. METHODS: This study tested var acidic terminal sequence-based (varATS) quantitative polymerase chain reaction (qPCR) for screening asymptomatic Plasmodium falciparum infections among dwellers of a sub-urban community in Lagos, Nigeria. Clinically healthy participants were screened for malaria using microscopy, RDT and varATS qPCR techniques. Participants were stratified into three age groups: 1-5, 6-14 and > 14 years old. RESULTS: Of the 316 participants screened for asymptomatic malaria infection, 78 (24.68%) were positive by microscopy, 99 (31.33%) were positive by RDT and 112 (35.44%) by varATS qPCR. Participants aged 6-14 years had the highest prevalence of asymptomatic malaria, with geometric means of ~ 116 parasites/µL and ~ 6689 parasites/µL as detected by microscopy and varATS, respectively. CONCLUSION: This study has revealed high prevalence of asymptomatic malaria in the study population, with varATS detecting additional sub-microscopic infections. The highest concentration of asymptomatic malaria was observed among school-age children between 6 and 14 years old. A large-scale screening to identify other potential hotspots of asymptomatic parasites in the country is recommended

A barcode of multilocus nuclear DNA identifies genetic relatedness in pre- and post-Artemether/Lumefantrine treated Plasmodium falciparum in Nigeria.

BACKGROUND: The decline in the efficacy of artemisinin-based combination treatment (ACT) in some endemic regions threatens the progress towards global elimination of malaria. Molecular surveillance of drug resistance in malaria-endemic regions is vital to detect the emergence and spread of mutant strains. METHODS: We observed 89 malaria patients for the efficacy of artemether-lumefantrine for the treatment of uncomplicated Plasmodium falciparum infections in Lagos, Nigeria and determined the prevalence of drug resistant strains in the population. Parasite clearance rates were determined by microscopy and the highly sensitive var gene acidic terminal sequence (varATS) polymerase chain reaction for 65 patients with samples on days 0, 1, 3, 7, 14, 21 and 28 after commencement of treatment. The genomic finger print of parasite DNA from pre- and post-treatment samples were determined using 24 nuclear single nucleotide polymorphisms (SNP) barcode for P. falciparum. Drug resistance associated alleles in chloroquine resistance transporter gene (crt-76), multidrug resistance genes (mdr1-86 and mdr1-184), dihydropteroate synthase (dhps-540), dihydrofolate reductase (dhfr-108) and kelch domain (K-13580) were genotyped by high resolution melt analysis of polymerase chain reaction (PCR) fragments. RESULTS: By varATS qPCR, 12 (18.5%) of the participants had detectable parasite DNA in their blood three days after treatment, while eight (12.3%) individuals presented with genotypable day 28 parasitaemia. Complexity of infection (CoI) was 1.30 on day 0 and 1.34 on day 28, the mean expected heterozygosity (HE) values across all barcodes were 0.50 ± 0.05 and 0.56 ± 0.05 on days 0 and 28 respectively. Barcode (π) pairwise comparisons showed high genetic relatedness of day 0 and day 28 parasite isolates in three (37.5%) of the eight individuals who presented with re-appearing infections. Crt-76 mutant allele was present in 38 (58.5%) isolates. The mdr1-86 mutant allele was found in 56 (86.2%) isolates. No mutation in the K-13580 was observed. CONCLUSIONS: Persistence of DNA-detectable parasitaemia in more than 18% of cases after treatment and indications of genetic relatedness between pre- and post-treatment infections warrants further investigation of a larger population for signs of reduced ACT efficacy in Nigeria