Kariya ga ƙarfen ƙarfafawa daga lalata
Bisa ga Eurocodes na yau, an ƙayyade mafi ƙarancin kaurin murfin kariyar kankare (cnom). Kaurin irin wannan murfin kankare shi ne mafi ƙarancin nisa daga saman waje na sashen ƙarfe mai ƙarfafa kankare zuwa ƙarfafawa ta farko. A sassan layi, wannan shi ne igiyar ɗaurewa, kuma a sassan farfajiya, wannan shi ne ƙarfin tsawon ƙasa na ƙasa. An bayyana murfin kariya na ƙididdiga kamar haka: cnom = cmin + Δcdev
cmin shi ne mafi ƙanƙantar rufin kariya da aka wajabta, wanda darajarsa ke dogara da yanayin mannewar kankare da ƙarfe na ƙarfafawa, yanayin muhalli, murfin da ke kan ƙarfen ƙarfafawa, da dai sauransu. Δcdev daraja ce da ke wakiltar karkacewar aiwatarwa. Dangane da matakin bayyanar da abin ƙarfen ƙarfafawa na kankare yake da shi, akwai ƙimomi daban-daban na rufin kariya na ƙididdiga; yawanci yana tsakanin 2,5 cm zuwa 3,5 cm. Ga tushe ana ɗauka cewa 5cm.
Halayen turmin siminti da kankare a lokacin yawan zafi da sanyaya
Ana iya ƙara ƙarfin sabon kankare da sauri ta hanyar dumama shi a hankali da tururi ko ta ajiye shi a cikin ruwa da ake ƙara masa zafi a hankali, sannan a bar shi ya huce a hankali. Ta wannan hanya, bayan aiki na kwana ɗaya, ana samun ƙarfin da a tsarin al’ada ake samu ne bayan makonni da yawa. Matsayin tasiri yana dogara da siminti da nau’in ƙwayar haɗawa, amma tare da kankare mai rauni ana samun sakamako mafi kyau fiye da na kankare mai mai.
Idan ana yin dumama da sanyaya cikin manyan iyakoki, za a samu manyan matsalolin damuwa a cikin kashi na kankare idan ana aiwatar da dumama da sanyaya da sauri. A irin wannan yanayi, musamman idan ana maimaitawa sau da yawa, ya kamata a yi la’akari da bayyanar ƙananan tsage-tsage da ke ratsa daga waje zuwa ciki suna shafar siffofin injina na kankare. A nan, siminti daban-daban suna nuna halaye mabambanta, saboda haka don amfani a aikace ana ba da shawarar zaɓar siminti a hankali.
Wucewar zafi ta siminti
Ƙimar ƙarfin watsa zafi na kankare na dogara da halayen ƙwanƙwasa da siminti, yawan siminti, yawan ruwan hadawa, danshin kankare, da kuma matakin zafin jiki. Ta gwaje-gwaje da alluna masu kaurin 10 cm da kuma kankare da aka busar sosai, an gano cewa ƙimar ƙarfin watsa zafi λ tana kaiwa 1,163 W/mK a 10 oC, kuma da allunan kankaren da aka bar a cikin ruwa tana kaiwa har 2,326 W/mK. Alluna masu kauri sun ba da ƙarin ƙimomin ƙarfin watsa zafi; mafi girman ƙima ya kai 2,38 W/mK.
Faɗaɗawar kankare saboda zafi
Faɗaɗawa da yawa tana dogara sosai da aggregate, sannan da danshin kankare, haka nan kuma da siminti kansa. Iyakokin da aka sani zuwa yanzu a 0 zuwa 40 oC sun kai kusan 6 zuwa 13*10-6 m/m ga kowane digiri.
Juriya ga lodin maimaituwa
1. Ƙarfin matsawa a lokacin gajiya. An yi amfani da ra’ayin ƙarfin gajiya a nan a ma’anar gaba ɗaya; don amfani na fasaha ya kamata koyaushe a bayyana ƙarfin gajiya (matsawa, ja, sauyawar matsawa da ja, lankwasawa, yanke, tsantsar yanke, lanƙwasawa) da kuma yanayin ɗaukar nauyi (kawai a kwance, kawai a maimaita, wani ɓangare a kwance kuma wani ɓangare a tsaye).
Ƙarfin matsawa a gajiya saboda ɗaukar nauyi a hankali: ya kamata a yi tsammanin cewa juriya ga nauyi na dogon lokaci ya kai aƙalla ¾ na ƙarfin da ke bayyana a gwajin matsawa na yau da kullum.
Ƙarfin matsawa a gajiya sakamakon maimaitattun nauyaya (asalin ƙarfin dinamik): an gano cewa asalin ƙarfin matsawa na dinamik na ginshiƙan kankare masu ƙira dabam-dabam, musamman waɗanda ke da adadin siminti daban-daban da kuma girman ƙwayoyi daban-daban, yana kaiwa aƙalla 0,5 na ƙarfin prism a ƙarƙashin nauyi na yau da kullum har zuwa karyewa. A nan an yi 260 zagayen ɗaukar nauyi a cikin minti ɗaya; jimillar adadin zagayen da aka yi ƙayyade wannan asalin ƙarfin dinamik ɗin ya kai miliyan biyu. Da yawan zagayen a minti ɗaya ya ƙaru (an gwada daga 10 zuwa 450 zagaye a minti ɗaya), haka kuma yawan maimaitawa da ke kaiwa ga karyewa ya ƙaru.
Ƙarfin matsawa a gajiya sakamakon aiki lokaci guda na lodin tsayayye da lodin maimaituwa: Idan aka ƙara lodin tsayayye ga lodin maimaituwa, to, da ƙara lodin tsayayyen, ƙimar amplitud na lodin maimaituwa da ake maimaitawa sau miliyan biyu ta ragu. Misali, sl. 1 yana nuna cewa amplitud ɗin lodin maimaituwa S sun kai:
- a ƙarƙashin nauyi na kwantar hankali domin σu = 6 kg/cm2 S = 109 kg/cm2
- a ƙarƙashin lodi mai natsuwa domin σu = 118 kg/cm2 S = 39 kg/cm2
- a ƙarƙashin lodi mai natsuwa ga σu = 157 kg/cm2 S = 8 kg/cm2
Hoto. 1
Fig. 2
2. Ƙarfin lanƙwasawa na kankare a lokacin gajiya. Gwaje-gwajen da aka nuna a fig. 2 ga katako da aka riƙe cikin yanayi mai ɗanshi a dindindin, sun nuna, a ƙarƙashin asalin ɗaukar nauyin dinamik cewa ƙarfin lanƙwasawa a lokacin gajiya ya kai 28 kg/cm2, yayin da ƙarfin lanƙwasawa na yau da kullum ya kai 53 kg/cm2, wanda ya dace da dangantaka 0,53.
Kankare mai sauƙi
Laka mai sauƙi (beton mai nauyi ƙasa da 18 kN/m3) ana samu ne ta amfani da ƙananan aggregati masu rami kamar su: pumice, slag daga manyan tanda, slag ɗin tukunyar jirgi, sannan kuma ta amfani da turmi daga yashi na halitta ko na ƙera da garin da aka gauraya da ƙari wanda yayin shirya turmi ke fitar da iskar gas (gas-concrete) ko kuma ke haifar da kumfa a turmi (foamed concrete).
Kankare mai nauyi kaɗan, daga cikin wasu abubuwa, ana amfani da shi sosai wajen ƙera tubalan gini da faranti na pumis domin bango da rufi; a busasshen yanayi ba ya ɗaukar zafi da kyau; ƙarfinsa matsakaici ne, amma yana sauƙin daidaituwa, don haka za a iya ƙera tubalan masu nauyi kaɗan domin bangon ɗaukar nauyi na gine-ginen zama cikin tabbaci.
Ana amfani da foda na aluminium a matsayin abin haifar da iskar gas a cikin kankaren gas. Dangane da yawan ƙazanta da sauran yanayi, ana samun abu mai cike da ramuka fiye ko ƙasa da haka, mai nauyin busasshe kusan 3 kN/m3 zuwa sama.
1. Nauyin ƙima na kankare mai sauƙi. Tare da pumice na halitta ana iya tabbatar da nauyin ƙima – ana nufi a yanayin da aka busar zuwa 105 oC – tun daga 7 kN/m3 zuwa sama, tare da ƙarfin matsawa na 2 MPa. Nauyin ƙimar da ake iya tsammani kusan shi ne jimillar taraɗɗen ƙwari da siminti a yanayin da aka tara su a kwano. Kankaren gas mai nauyin ƙima sama da 8 kN/m3 a ƙa’ida bai dace da fasaha ba.
2. Ƙarfin matsawa na kankare mai nauyi kaɗan. Ga kankaren zubawa, ba tare da wasu matakai na musamman ba ana iya samun ƙarfi har zuwa 8 MPa, kuma da tsakuwa har ma zuwa 12 MPa. Ana buƙatar gwaje-gwajen dacewa akai-akai. Kankaren mai ramuka (kankaren gas da kankaren kumfa) ya dace da bangon ɗaukar kaya ne kawai bayan ya ƙara ƙarfi a ƙarƙashin matsin tururi. Tare da albarkatun ƙasa masu dacewa, ana iya tabbatar da nauyin ƙima na 6 kN/m3 da ƙarfin matsawa na 5 MPa.
3. Ƙarfin lankwasawa na kankare mai haske. Dangantaka tsakanin ƙarfin lankwasawa da ƙarfin matsawa ta nuna a cikin iyakokin buƙatun aikace-aikace cewa tana da girma ƙwarai, amma yayin da ƙarfi ke ƙaruwa wannan dangantaka tana raguwa.
4. Matsayin raguwa na kankare mai sauƙi. Matsayin raguwa ya danganta galibi da taurin aggregate, haka kuma da yawan abin da ya ƙunshi simintin da ya yi tauri; raguwar kankare mai sauƙi ta fi raguwar kankare na tsakuwa. Kankaren da aka yi da ɓarkakken bulo ya nuna a cikin shekara guda jimillar matakin raguwa kusan 0,65 mm/m. Abubuwan da aka kawo sabo na natural pumice, a cikin 14 m watanni, sun taƙaitu da kusan 0,8 mm/m. Samfuran kankaren iskar gas da kumfa da suka yi tauri a iska sun nuna raguwa mafi yawa ƙwarai, har ma sama da 2 mm/m. Bai kamata a manta ba cewa duk wani kankare yana kumbura lokacin da ruwan sama da dusar ƙanƙara mai narke suka jika shi, sannan daga baya yayin bushewa kuma yana sake raguwa.
Hoto. 3
5. Ƙimar yanayin ɗaukar zafi. Ƙimar yanayin ɗaukar zafi tana raguwa da nauyin ƙimarsa a girma, kuma a sauran yanayi iri ɗaya tana ƙara raguwa gwargwadon yadda ramukan iska suke ƙanana kuma an rarraba su daidai. Ga kankaren cike da busasshiyar iska, ya kai (λ = 0,4625 ga 9 kN/m3; λ = 0,58 – 0,7 ga 12 kN/m3; λ = 0,81 – 1,05 ga 16 kN/m3). Ga kankaren gas mai bushewar iska, bayanai suna a sl. 3.
LURA:
- 0,1 kcal/mhoC = 0,1163 W/mK
- 0,1 kg/dm3 = 100 kg/m3 = 1 kN/m3